When family members are also co-workers, things can get messy. This is never truer than in royal families, where the interplay of private passions and public displays of affection or dissatisfaction are broadcast on an international stage. While some royal feuds remain minor, others in history have become so dysfunctional, they’ve led to major wars.

By the time the legendary Cleopatra VII was born into the ruling Ptolemy dynasty of Egypt around 69 B.C., the family already had an incestuous, murderous history. For generations, sisters had killed brothers, mothers had gone to war with their children, and sons had murdered their parents.

“After a while the butchery came to seem almost preordained,” writes Stacy Schiff in Cleopatra: A Life. “Cleopatra’s uncle murdered his wife, thereby eliminating his step-mother (and half-sister) as well.”

The last of their line, Cleopatra and her three siblings continued this bloody family tradition. On the death of their father around 51 B.C., Cleopatra and her brother, Ptolemy XIII, were married and assumed the Egyptian throne as co-rulers. This forced partnership quickly fell apart, and by 48 B.C., Ptolemy XIII and Cleopatra were engaged in a brutal civil war against each other. In the midst of the madness, their younger sister, Arsinoe IV, also claimed the throne for herself.

Cleopatra did not take her sister’s betrayal lightly. “It is unlikely that she underestimated her 17-year-old sister,” writes Schiff. “Arsinoe burned with ambition; she was not the kind of girl who inspired complacency.”

Arsinoe soon banded together with Ptolemy XIII and together the siblings launched the Siege of Alexandria against Cleopatra in the winter of 48 B.C. But Cleopatra then gained a secret weapon—the all-powerful Roman leader Caesar, with whom she began a personal and professional relationship. Together, they routed her siblings at the Battle of the Nile, in 47 B.C.

Ptolemy XIII drowned in the Nile shortly after his defeat. Arsinoe was captured and paraded through Alexandria in golden shackles, before being exiled to the Temple of Artemis in Ephesus.

Her triumphant sister, Cleopatra, now in control of Egypt and Caesar’s heart, soon married her younger brother Ptolemy XIV.  Ptolemy XIV then died in 44 B.C., likely poisoned by Cleopatra, and the queen made her infant son co-ruler with her as Ptolemy XV Caesar.

But there was still the problem of Arsinoe. According to Schiff, Cleopatra’s younger sister rallied enough support in Ephesus to have herself proclaimed queen of Egypt. “Her feat speaks both to her tenacity and to the fragility of Cleopatra’s position outside her country,” Schiff writes, “certainly the two sisters despised each other.”

This prolonged family feud finally ended in 41 B.C., when Cleopatra’s great love Mark Antony ordered Arsinoe killed on the steps of the Temple of Artemis. “Now,” wrote one chronicler, “Cleopatra had put to death all her kindred, till no one near her in blood remained alive.”

There is only one civil war in history that can trace roots to a chamber pot.

When William the Conqueror, the first Norman King of England, died in 1087, he left Britain to his middle son William Rufus instead of his eldest son Robert. William had long been in conflict with the charming, combative and dissipated Robert (known as Robert Curthose, perhaps for his short legs).

According to an account by Orderic Vitalis, a Benedictine monk who wrote chronicles of 11th and 12th centuries, Robert had been at odds with his father since 1077, when William Rufus and their younger brother Henry had dumped a full chamber pot over his head. A brawl ensued, and their father broke it up, but refused to punish William Rufus and Henry. Robert was furious and staged a failed attack on the castle of Rouen in retaliation.

This family feud lasted for years, with Robert fleeing to Flanders, fighting his own father in combat. They were finally reconciled in 1080, but not surprisingly, their relationship was strained, and Robert spent most of his time abroad. When his father died, Robert was left the lesser prize of Normandy. He gathered a rebellion against his brother, now King William II, but it failed when Robert failed to appear in England.

Instead, he went off to crusade in the Holy Land. On his way back in 1100, he was informed that King William II had died—and that his young brother Henry I had claimed the crown.

From Normandy, Robert raised an army and headed across the channel in July 1101. “Robert headed towards London and was intercepted by Henry at Alton in Hampshire,” writes historian Richard Cavendish. “Henry persuaded Robert to renounce his claim to England in return for a pension of 3,000 marks a year and the abandonment of any claim on Henry’s part to Normandy. It was agreed that no action would be taken against the Duke’s supporters.”

But Robert had been deceived. His brother stopped sending the pension and invaded Normandy, restless after years of Robert’s mismanagement. In 1106, Henry beat his brother at the Battle of Tinchebray. Robert was imprisoned for the next 28 years. “Woe to him that is not old enough to die,” he wrote during this long captivity.

Robert finally died in 1134, in Cardiff Castle, at the ripe old age of 80. Henry I died the following year, victorious over his brother even in death.

When Mary I finally inherited the throne of England in 1553, she had endured a lifetime of disappointments, heartbreaks and slights. The only child of King Henry VIII and the Catholic, saintly Catherine of Aragon, she had been the beloved heir to her father’s throne for much of her childhood.

But after Henry’s passionate affair and subsequent marriage to the Protestant-leaning Anne Boleyn, her world was destroyed. She was ripped away from her mother, stripped of her royal title and forced to curtsey to her new half-sister, a small redheaded baby—Princess Elizabeth.

Her new stepmother was particularly cruel to young Mary, and the impressionable teenager stored away these insults for the rest of her life. After Anne Boleyn’s execution in 1536, Mary’s status was restored, and she appeared to become fond of her now motherless half-sister Elizabeth.

But their tortured familial history was only part of what would make this ceasefire temporary. “Relations between elder and younger sisters are often difficult—particularly when there is an age gap of seventeen years, as there was to be between Mary and her half-sister Elizabeth,” writes David Starkey in Elizabeth: The Struggle for the Throne. “But fate also cast them as opposites in appearance and character and opponents in religion and politics.”

With the vehemently Catholic Mary’s accession in 1553, all her old bitterness rose to the surface. Though Elizabeth had ridden into the city of London with Mary for her coronation, their relationship quickly soured. Elizabeth was now the “second person” in the kingdom—young, charismatic, confident and Protestant.

READ MORE: What Inspired Queen 'Bloody' Mary's Gruesome Nickname?

In 1554, the Wyatt Rebellion was launched in reaction to Mary’s unpopular plan to marry the Catholic King Philip of Spain. Leaders of the rebellion planned to put Elizabeth on the throne, and Mary believed that her sister had been part of the plot. Elizabeth was arrested and sent to the ominous Tower of London, the same place her mother had been executed decades before. “Oh Lorde!” she cried. “I never thought to have come in here as prisoner!”

Once in the tower, Elizabeth wrote her sister a frantic, rambling letter, her usual composure lost to fear:

I pray to God the like evil persuasions persuade not one sister against the other, and all for that they have heard false report, and the truth not known. Therefore, once again, kneeling with humbleness of heart, because I am not suffered to bow the knees of my body, I humbly crave to speak with your Highness, which I would not be so bold as to desire if I knew not myself most clear, as I know myself most true.

The letter did not have its intended effect. Mary was further enraged by this letter, feeling that it lacked the respect she deserved. However, she did let her sister out of the Tower after three weeks, and Elizabeth was sent to Woodstock under house arrest. Here, she etched a short poem into the window of her prison with a diamond:

Much suspected by me,

Nothing proved can be,

Quoth Elizabeth prisoner

Elizabeth was finally pardoned a year later, and the sisters resumed a strained but cordial public relationship. Only four years later, in 1558, Mary died during an influenza epidemic, and Elizabeth started her glorious reign.

From childhood, the clumsy, well-meaning Louis XVI of France was often overshadowed and outmaneuvered by his malicious younger brothers. Stagnant and bored at the court of Versailles, Comte de Provence and Comte d’Artois spent much of their time stirring up gossip about their hapless older brother.

Left to their own devices, the brothers often engaged in petty arguments, occasionally in view of the whole court. Soon after Louis’s marriage to the young Marie Antoinette in 1770, the former Austrian archduchess—from a large family of brothers and sisters—found herself frequently breaking up embarrassing fracases between the brothers.

“With her experience of family life,” Antonia Fraser writes in Marie Antoinette: The Journey, “Marie Antoinette began to act as peace-maker between the sparring royal brothers, Louis Auguste and Provence. On one occasion when the clumsy Louis Auguste broke a piece of porcelain belonging to Provence and the younger brother flew at him, Marie Antoinette actually interrupted the fight...”

With their accession to the throne in 1774, Louis and Marie Antoinette’s inability to produce an heir became fodder for his brothers’ taunts. After his own marriage, Provence was also unable to consummate his union. “None of this,” writes Fraser, “stopped the wily Provence from dropping hints about his wife’s condition whenever he could most conveniently bait his brother and his Austrian wife with their own failure.”

The brothers also encouraged the rumor that the graceful, fun-loving Marie Antoinette was having an affair with the equally high-spirited Artois, a complete fabrication. This assault on their brother’s fertility reached a breaking point in 1778, with the birth of Princess Marie-Therese. According to Fraser, at the child's baptism, the Comte de Provence argued that the "name and quality" of the parents had not been formally given.

"Under the mask of concern about correct procedure, the Comte was making an impertinent allusion to the allegations about the baby’s paternity," Fraser writes.

As tensions rose in France, his brothers’ increasingly conservative, reactionary politics caused constant problems for the moderate, placating Louis XVI. Both Provence and Artois escaped France with their families during the revolution. After their brother’s death, both men eventually got what they had perhaps always longed for—the chance to be king. After the fall of Napoleon, Provence reigned as Louis XVIII from 1814 to 1824. Artois followed as Charles X from 1824 to 1830, before he was deposed.

"My relations," Napoleon once said, "have done me more harm than I have done them good."

The fallen Emperor had reason to be bitter. In Napoleon’s eyes, he had raised his large Corsican brood, consisting of Joseph, Lucien, Elisa, Louis, Pauline, Caroline and Jerome, to the status of royalty. He had given them titles, put them on the thrones of kingdoms, and made them rich. In return, Napoleon had expected blind loyalty from his siblings. He should have known better.

From the start, not all of Napoleon’s brothers and sisters held him in high regard. His younger brother Lucien hated him from childhood, believing that he was a bully and a megalomaniac. Writing to his older brother Joseph in the early 1790s, he listed all Napoleons faults, noting, "He seems to me to have a strong liking for tyrannical methods; if he were king, he would be a tyrant, and his name, for posterity and in the ears of sensitive patriots, would be a name of horror."

Once Napoleon took power in France, Lucien was banished to Italy for marrying a woman whom his brother did not approve. The rest of the Bonapartes continued to bicker—united in little but their hatred of Napoleon’s wife, Josephine. In response, Napoleon taunted them with the honors he bestowed on Josephine and her children. One night at dinner, he continually addressed his stepdaughter Hortense as Princess, just to anger his sisters. According to Theo Aronson, author of _The Golden Bees: The Story of the Bonapartes, "_Caroline burst into tears. Elisa, who had a better grip on her emotions, resorted to shafts of biting sarcasm and long haughty silences."

The dysfunction reached a fever pitch in 1804, when Napoleon crowned himself Emperor. His sisters and sisters-in-law were appalled that they would have to carry the hated Josephine’s train in the ceremony at Notre Dame. Joseph said he would move to Germany if his wife was so dishonored. Eventually, the women begrudgingly agreed—only if their trains were also carried.

The siblings were also jealous of each other. Napoleon made Joseph King of Italy and Sicily, Jerome King of Westphalia, and Louis King of Holland. Upon learning that Elisa had been given the principality of Piombino, Caroline quipped, "So Elisa is a sovereign Princess, with an army of four privates and a corporal."

After his defeat at Waterloo, Napoleon turned against much of his family. "I love no one, no, not even my brothers," he once said. "Joseph, perhaps a little; and if I do love him, it is from habit, and because he is my elder."

Stewing in exile on Saint Helena he realized he had made a mistake by putting his siblings in positions of power. "If I made one [of my brothers] a king,” he muttered, according to Aronson's account, “he imagined that he was king by the grace of God. He was no longer my lieutenant; he was one enemy more for me to watch."