Mary Boleyn is the least known of the Boleyn family of Hever Castle , a woman almost forgotten by history, but she was the favourite mistress of one of the greatest Kings of England. I discovered her while researching for The Other Boleyn Girl, and her story drew me to Hever Castle .

The house was bought by her grandfather, a draper in Ipswich who climbed the difficult slope to be Mayor of London, and married his son Thomas, to a daughter of the powerful Howard clan.

When Sir Thomas inherited Hever Castle it was still a medieval hall. He made it into a more comfortable house suitable for the peaceful Tudor years. Elizabeth Howard must have been comforted that though her husband did not come from a family as grand as her own, at least he could provide for her.

The couple had only three children who survived to adulthood. Like most aristocrats of the time, the children were sent away to be taught the skills of the royal court. A marriage was arranged for Mary to one of Henry VIII's courtiers when she was only 12.

In a court completely ruled by the whim of the King, the only way for a family to advance was to take his favour. The Boleyns and their kin the Howards would have been delighted when the King took Mary as his mistress. Mary became pregnant and gave birth to a daughter, Catherine and a year later to a boy, Henry.

While Mary was spending the compulsory six weeks in the darkened rooms of childbirth, Anne Boleyn stole her sister's lover and pushed Mary into the margins of history.

While Anne rose to be Queen of England Mary all-but disappeared. She fell in love with a young man of no fortune named William Stafford. It must have been inescapable desire on both sides since they risked everything to marry. When Queen Anne discovered her sister was married and pregnant she banished her from court.

History is often ironic. Mary, the discarded mistress, survived the treason trial which executed her brother and her sister and was the death of the ambitions of her family. Her father and mother died within two years. Their beautiful Hever Castle was taken by the King. But Mary and the despised William Stafford inherited the other Boleyn House: Rochford Hall, in Essex and lived to a contented old age.

Hever Castle was given to Anne of Cleeves - Henry's fourth wife who was rejected almost on sight by the irascible King. She lived a quiet life in the country, caring occasionally for the royal princesses and insisting on the very best food from the Hever kitchens.

In yet another twist to the story Catherine, Mary Boleyn's daughter, was appointed as companion to Anne of Cleeves, and lived with her at Hever. Catherine would have been well aware that this was her great grandfather's house and that the family fortunes had tumbled very low indeed, when she was a lady in waiting in a house which had once been owned by her family.

Tracing Mary Boleyn's story was like being a detective. She sometimes appears in the histories, in the margins, but many books do not even mention her. One of the great pleasures of trying to find her was visiting her homes.

The prettiest of all of them was Hever Castle . Although it is much changed, I was able to imagine Mary walking over the drawbridge, under the portcullis into the entrance courtyard, a wonderfully evocative space.

George Boleyn's little room, with the flickering reflection from the waters of the moat on the ceiling, is a poignant reminder of the young man, his family's only heir, who was drawn into his sister's disgrace and died for it.