Queen Elizabeth I of England and Mary, Queen of Scots were two of the greatest, most legendary rivals in recorded history—although they never even met. In one castle was Elizabeth, the childless “virgin” queen: bawdy, brilliant, tactical and cynical. On the other, Mary: feminine, charming, romantic and reckless.

Their decades-long verbal boxing match over the English crown would end with Mary’s beheading at Fotheringhay Castle—with Elizabeth’s blessing—in 1587. But the two cousins’ tortured relationship was determined long before, during childhoods so dissimilar and defining that they would inform both Queens’ characters—and seal Mary’s tragic fate.

Elizabeth, daughter of the mercurial King Henry VIII and his second wife, Anne Boleyn, was born on September 7, 1533, at Greenwich Palace. Though Anne had bewitched the King, she was despised by most of the court and the public. Her redheaded daughter was considered the “bastard child of a whore.”

Henry VIII had cast aside his universally respected Catholic wife, Catherine of Aragon, and their daughter, Mary, for Anne. He also broke with the Catholic Church when the Pope refused to validate his marriage to Anne. But the turmoil would be justified if Henry’s “concubine” produced the male heir that the King and kingdom had long prayed for.

It was not to be. “The King’s mistress was delivered of a girl, to the great disappointment and sorrow of the King, and of the Lady herself,” Eustace Chapuys, the hostile ambassador to the Holy Roman Empire, wrote, “and to the great shame and confusion of physicians, astrologers, wizards, and witches, all of whom affirmed that it would be a boy.”

This disappointment and her subsequent inability to produce a son hastened the spectacular fall of Anne Boleyn. Although it is unknown whether three-year-old Elizabeth was aware of her mother’s execution in 1536, it appears the precocious, watchful girl was quick to notice the dramatic change in her station. “How haps it Governor,” she asked in 1537, “yesterday my Lady Princess, and today but my Lady Elizabeth?”

And so, the newly-styled Lady Elizabeth was declared illegitimate and coldly hidden out of her father’s sight, with a small household and little income. Things got so bad that the year of her mother’s death, Elizabeth’s governess pleaded for money, complaining the child “hath neither gown, nor kirtle, nor petticoat.”

Elizabeth’s childhood was not totally devoid of comfort. She developed a devoted little court and a clutch of servants who would stay with her for decades. Governess Kat Ashley would be like a mother to Elizabeth, taking "great labor and pain in bringing me up in learning and honesty."

The lonely child received a superior education. “The constitution of her mind is exempt from female weakness,” her tutor Robert Ascham would write. “She is endued with a masculine power of application. No apprehension can be quicker than hers, no memory more retentive.”

Elizabeth was occasionally brought to the English court where she impressed her distant father with her intellectual prowess. She also developed a relationship with her stepmother, Henry’s fifth wife, Katherine Howard, only to see the flighty teen executed by her father in 1542. It is said that this was the incident that prompted the practical nine-year-old to vow she would never marry.

That same year, another ginger-haired princess was born on December 8 at Linlithgow Palace in Scotland. The frail infant, named Mary Stuart, was the only surviving child of the equally weak King James V of Scotland and his formidable wife, Mary of Guise. The child (Henry VIII’s niece) was Queen of Scotland nearly from birth since her father died when she was only six days old. She was also raised to believe she was the lawful, rightful heir to the British throne.

“Mary’s sense of herself as queen had been with her from the dawning of her consciousness,” biographer Jane Dunn writes in Elizabeth and Mary: Cousins, Rivals, Queens. “It was never disputed or tested, as was Elizabeth’s. This awareness of her pre-eminence was her companion through life, something taken for granted, the responsibilities to which she did not apply much profound thought nor, in the end, much value.’’

The baby queen spent her first five years being moved from one palace to another in Scotland to keep her safe from the warring clans of the highlands. In 1548, when Mary was sent to her mother’s homeland of France to become the fiancée of the Dauphin, she was already a figure of romance and sympathy. For the next 13 years, the little Dauphiness- Queen would be worshipped by both the French royal family and her mother’s powerful family.

“The little Queen of Scots is the most perfect child that I have ever seen,” King Henry II of France proclaimed soon after meeting his new charge (Mary of Guise had stayed in Scotland to rule her daughter’s domain). His son, the sickly, despondent Francis, also adored his future wife and hung onto her every word.

Since Mary was already an anointed Queen, she walked before any of the French princesses, even the King’s own daughters. “It is impossible,” Mary’s doting grandmother wrote, “for her to be more honored than she is.”

“While her cousin Elizabeth’s youth was largely spent outside court life with her books and plans, and the occasional visitor to engage her thoughts,” writes Dunn, “Mary’s life from the age of six was lived at the very center of the most glamorous court in Christendom.”

Mary spent her childhood surrounded by cousins, slavish servants, tutors and pets. Her bills show that she had a lavish wardrobe the young Elizabeth could only have dreamed of, as well as dancing, horseback riding and singing lessons.

“In marked contrast to her cousin Elizabeth Tudor, Mary Stuart enjoyed an exceptionally cosseted youth,” Antonia Fraser writes in her biography Mary, Queen of Scots. “It is left to the judgment of history to decide whether it did, in fact, adequately prepare her for the extreme stresses with which the course of her later life confronted her.”

While the pretty, well-spoken Mary flourished, secure in her majesty, the stresses of royal life were almost crushing her cousin Elizabeth. After her father’s death in 1547, Elizabeth’s younger brother, Edward VI, ascended the throne. The teenage Elizabeth, long restored to the title of Princess, should have enjoyed a relatively benign fate. She was placed in the care of the learned Catherine Parr, her father’s last wife, with whom she had become very close.

However, the arrangement would end in disaster. Parr had married Thomas Seymour, brother of the Lord Protector of England, less than a year after Henry VIII’s death. Seymour was sexually inappropriate with Elizabeth, with his wife sometimes joining in. When confronted about his actions by Elizabeth’s governess Kat Ashley, he excused it as a bit of fun.

Elizabeth was sent away in disgrace, and her relationship with Seymour continued to haunt her. In 1549, the recently widowed Seymour was arrested for treasonous behavior; many believed he intended to marry Elizabeth and claim the throne in her name. To prevent this, Elizabeth was quarantined, and her beloved governess was thrown in jail.

On the day of Thomas Seymour’s execution, she supposedly stated: “This day died a man with much wit and very little judgement.”

Worse was to come. In 1553, Elizabeth’s half-sister,  Mary Tudor (Catherine of Aragon’s Catholic daughter) became England's first female monarch. Elizabeth now took the position of “second person” in the country, causing her sister—who later became known as "Bloody Mary"—great anxiety.

According to many, Mary I had always despised her Protestant half-sister. In 1554, the Protestant Wyatt’s Rebellion, which focused on securing the throne for Elizabeth, finally gave Mary the onus to unleash her pent-up rage against her relative. Elizabeth was thrown into the Tower of London, where her mother Anne Boleyn had died. As she entered, she cried out to the hundreds of Londoners who had come out to show her support, “Oh Lorde! I never thought to have come in here as prisoner!”

“The horror of her incarceration in the Tower was a defining event Elizabeth could never forget,” Dunn writes. After three weeks in prison, Elizabeth was banished for almost a year before Mary pardoned her.

When Elizabeth finally became Queen in 1558, she had already lived through several lifetimes. “I did put myself to the school of experience,” she said decades later, “where I sought to learn what things were most fit for a king to have, and I found them to be four: namely, justice, temper[ance], magnanimity, and judgement.”

However, many of Elizabeth’s Catholic subjects believed that Mary, Queen of Scots was the rightful queen of England since she was the senior descendant of Henry VIII's elder sister.

Three years after Elizabeth became Queen, Mary returned to her Scottish kingdom, newly widowed after a short reign as Queen consort of France.

The coddled royal was neither prepared for the coarse Scots, nor the coldness of her cousin Elizabeth. As the “second person” in the line of succession, she expected Elizabeth to name her heir to the British throne. But Elizabeth refused to formalize the arrangement.

Mary’s second marriage was to her first cousin, Henry Stuart, Lord Darnley, a match that enraged Elizabeth I, who had not been asked permission for the marriage. After Darnley’s assassination, Mary wed James Hepburn, Earl of Bothwell, who may have been responsible for Darnley’s murder. The public found the marriage shocking, and Mary was denounced as as an adulteress (Bothwell had been married previously, so Catholics considered the marriage to Mary unlawful) and a murderer. Soon, Mary was forced to abdicate the Scottish throne in favor of her one-year-old son and imprisoned.

For Mary, her 19 years in captivity would be dull and repetitive, as she was shuffled from one minor English castle or manor to another. Due to her rank, Elizabeth demanded Mary be kept in relative luxury with a small retinue of loyal servants to keep her company. But her years of boredom gave Mary ample opportunity to write her cousin letters, hoping to convince Elizabeth that they could be partners instead of enemies.

“Little is known of Elizabeth’s inner feelings for Mary,” Fraser writes, “since the English queen had learned in childhood to hide all inner feelings, those dangerous traitors, within the breast.”

However, when Mary’s involvement in the Babington Plot to assassinate Elizabeth and take the English throne was discovered, Elizabeth signed Mary’s death warrant with a flurry of other papers and wished for her cousin's execution to take place without her knowledge.

It was nothing personal: in Elizabeth’s mind, her hard-won crown—and therefore the security and prosperity of England itself—was in jeopardy if Mary stayed alive.

Mary, Queen of Scots was convicted of treason on October 25, 1586. She was executed by beheading on February 8, 1587, at Fotheringhay Castle, a week after Elizabeth signed the death warrant for the troublesome cousin she had never met.

Since her birth, Elizabeth had repeatedly been taught the most important lesson for any successful royal ruler. Almost all relationships—especially familial ones—are in the end, only political.