Elizabeth I's rivalry with her Catholic cousin Mary, Queen of Scots is well known. But for her first ten years as queen, she feared her Protestant rivals and cousins still more, says historian Leanda de Lisle, who has brought them vividly to life

THE story of the sisters of the Nine Days Queen, Lady Jane Grey, was hidden by history. But as I discovered in my triple biography. The Sisters Who Would Be Queen, they were the rightful heirs to Elizabeth I. Now novelist Philippa Gregory, who lives in North Yorkshire, tells me "I have used your excellent history to guide me through the events", for her new blockbusting novel The Last Tudor. It is brilliant fiction, but knowing the true story makes it all the more extraordinary.

Imagine you are 18. Your elder sister has been executed after a short reign as queen. But you have survived the rule of her killer, ‘Bloody’ Mary Tudor and emerged as the heir to Elizabeth I: the last Tudor. Such was the fate of the second the three Grey sisters, Lady Katherine Grey.

To recover the real Katherine and discover why the story of the Grey sisters was later covered up, we must return to 1558, when Elizabeth I was about to inherit the throne from Bloody Mary. Katherine was staying with her friend, Jane Seymour, in a country house where she fell in love with Jane’s 19-year-old brother, ‘Ned’ Seymour, Earl of Hertford.

Ned’s mother warned him their affair was dangerous. Under the will of Henry VIII, backed by English law, Katherine was Elizabeth’s heir. This is not, of course, how history remembers it. The Catholic Mary Queen of Scots is the Stuart cousin we recall as Elizabeth’s rival. But Henry VIII had demoted the Stuarts in favour of the royal line of the Grey sisters, who were also great grandchildren of Henry VII.

The eldest, Lady Jane Grey, was catapulted over the Tudor sisters, when she was left the throne by Henry’s son Edward VI. But less than two weeks after Edward’s death Queen Jane had been overthrown and was beheaded in 1554, aged 16.

The danger for Elizabeth I was that if she failed to marry and have sons, and Katherine did, then Elizabeth, in turn, could be overthrown. The English Protestant elite had backed Jane Grey before her death, and they now wanted a queen who was not only Protestant, as Elizabeth was, but would also have a son as a future king.

When Bloody Mary died in 1558, Queen Elizabeth knew nothing of Katherine’s love affair with Ned Seymour, but she made it plain she disliked the Grey girls and was determined neither Katherine, nor the youngest sister, the diminutive, Lady Mary Grey, would ever be allowed to marry.

Katherine defied the queen to marry Ned in secret with only his sister Jane Seymour, as witness. Remarkably, I found the details of what followed, down to the sexual positions of the wedding night, in original manuscripts.

The couple married in Ned’s bedroom at a house on the Thames. They briefly toasted their wedding, but Ned’s sister, ‘perceiving them ready to go to bed’ then left. They made love on one side of the bed and then the other with Katherine naked save for a fashionable headdress. They got up briefly and then went back, to make love again, before dashing back to court to avoid being missed.

Over the following months the couple met for sex in the Queen’s palaces and in Ned’s London house. It wasn’t until Katherine was eight months pregnant that the Queen found out about their secret marriage. The couple was sent to the Tower, but the Queen’s fury could not prevent Katherine giving birth to a prince of a new Seymour royal dynasty.

As Ned’s sister –the sole witness to the marriage – had died of typhoid, and the priest had vanished, Elizabeth had the Church of England decree the marriage had never taken place. Katherine’s son was made a bastard. Sympathetic warders in the Tower nevertheless allowed Ned to corridor creep to Katherine’s rooms on three occasions. Again manuscripts survive describing their love-making on the striped satin bed in her prison room. In 1563 Katherine gave birth in the Tower to a second son.

A furious Elizabeth had the new parents separated in far-flung country house prisons. In a unique Tudor letter, Katherine was frank about how much she missed their love-making. ‘I long to be merry with you, as I know you do with me, as we were when our sweet little boy was begotten [conceived] in the Tower’ she told Ned, ‘I wish you to be as happy as I was sad when you came to my door for the third time, and it was locked. Do you think I can forget what passed between us? No, I cannot. I remember it more often than you know... such is my boundless love for my sweet bedfellow, that I once lay beside with joyful heart and shall again’.

Although Katherine pleaded with the Queen for her forgiveness she was kept apart from Ned and her elder son.

A miniature of Katherine, painted at around this time by the female court artist, Levina Teerlinc, remains the earliest known portrait of an English mother with her baby: a sad reminder for Katherine of all she had lost.

The Virgin Elizabeth, eaten up by sexual jealously and fear of her rivals, even imprisoned the youngest sister, the tiny Lady Mary Grey, who married the huge guard in charge of palace security – a marriage to a commoner that ruled her out from ever becoming queen. She would not be released until her husband was dead.

Katherine, meanwhile, never would lie beside her Ned again, as she had dreamed she would. In January 1568 Katherine’s warder asked for the royal doctor to help the despairing twenty-eight year old. But Katherine said she had no wish to live. Instead she sent a message to Elizabeth begging her to ‘be good to my children and.. to my Lord [Ned], for I know my death will be heavy news to him’. She then asked her warder to send Ned a memento mori ring, engraved with the words, ‘While I lived, yours’.

Elizabeth put on a show of grief at Katherine's death, expected at the death of a relative, but it was judged unconvincing. ‘She was afraid of her’, the Spanish ambassador noted.

Ned was freed in 1571, still hoping his elder son would one day be King. But at 19 the boy fell in love with a commoner. Elizabeth gave this marriage her blessing knowing it would destroy the boy’s chances for the crown.

Katherine’s younger son pre-deceased Elizabeth, dying in 1600, and the way was left clear for Mary, Queen of Scots’ son, James Stuart, to succeed the last Tudor in 1603. Ned lived long enough to see how unpopular King James I became. He died aged 84, over 50 years after Katherine, having found in his last years, the priest who had married them and could prove their sons were legitimate.

The couple’s grandson, William Seymour, buried them together in a magnificent tomb in Salisbury cathedral. The engraved words celebrate the star-crossed lovers, kept apart by Elizabeth, but re-united in their graves.

For reasons of religious and dynastic politics the history of the Grey sisters was then deliberately forgotten. No one wanted to remember that Elizabeth, England’s most popular monarch, had destroyed her English heirs, in favour of a foreign Scot. Nor did the Stuarts want it remembered that they had come to the throne against English law in 1603 and in place of an English dynasty.

And so Elizabeth I, the last Tudor took to her grave the true story of the sisters who would be queen, a tale as intimate and extraordinary as a novel, but also absolutely true.

Leanda de Lisle is the author of the triple biography The Sisters Who Would be Queen, the Tragedy of Mary, Katherine & Lady Jane Grey, and the biography of the dynasty Tudor, The Family Story. She will be giving a talk at the Ryedale Festival, on Friday, 6pm-7pm. St Mary's Priory, Old Malton Road, Malton, YO17 7HB. Tickets: http://ryedalebookfestival.com