The Showgirl and the Prince is a new memoir by Edward's ex-girlfriend, Ruthie Henshall

Prince Edward's ex-girlfriend has admitted that she keeps in touch with the King's younger brother.

While clearing out boxes in her garage, West End star Ruthie Henshall stumbled upon old diaries and romantic correspondence from Prince Edward, sparking the idea for her forthcoming memoir.

Before putting pen to paper, the 59-year-old actress chose to give her former boyfriend advance notice of her plans.

"He thanked me," she told Hello!. "I didn't want to blindside him and I wanted to assure him that it wasn't a kiss and tell. My experience with him and his family was really rather lovely."

The pair maintain regular contact decades after their romance ended, chatting by telephone two or three times annually, with the Duke of Edinburgh never forgetting to ring on her birthday.

"Both our lives moved on, but we have a great friendship," Ms Henshall said.

"I have so much love for him and he has ended up with the right person, as has John Gordon Sinclair," she added. "I'm a complicated lady to have a relationship with, and so it gives me great joy to see two people I love so dearly still be happy with the perfect person for them."

The Showgirl and the Prince, published by Macmillan and priced at £22, arrives in bookshops on July 16.

Ms Henshall describes the work as "a love story set against the backdrop of the Eighties and Nineties of musical theatre."

"We had all the mega-musicals coming in and it was buoyant and brilliant," she told the magazine. "The experiences and the romance made it a very heady time."

The memoir chronicles her five-year relationship with the Duke of Edinburgh, now 62, which she characterises as "a very passionate affair."

The couple first crossed paths in 1988 when the prince was employed as a production assistant at Andrew Lloyd Webber's Really Useful Theatre Company.

Their romance flourished as Ms Henshall's career took off, with the talented performer from Bromley securing leading roles in Les Misérables, Miss Saigon and Crazy for You.

However, the demands of keeping their relationship hidden from the press, combined with their increasingly different professional paths, placed considerable strain on the partnership.

After several brief separations, they parted ways permanently following five years together, having accepted that Ms Henshall would never prioritise anything above her theatrical ambitions.

"I don't think I would have been a very good royal and I could never have sat there watching other people do what I love," she reflected.

The memoir offers glimpses into Ms Henshall's visits to Buckingham Palace, Sandringham, Windsor Castle and Balmoral, where she recalls consuming her first martini, which "knocked me off my feet."

She portrays the late Queen Elizabeth II as warm and surprisingly relaxed in family settings, noting that the monarch "was always friendly and welcoming because I think she could tell I was a friend of Edward's."

Princess Margaret left a particularly strong impression, with Ms Henshall calling her "a doll" and recalling how they connected over their mutual passion for theatre.

The actress also recounts performing the Les Misérables number I Dreamed a Dream at the royal dinner table before the late Queen and Princess Margaret, having been encouraged to sing by Princess Diana.