The Queen is the matriarch of one of the world's most powerful families. And through her reign, she has had the unwavering support of her husband, Prince Philip - or has she?

A new book by British author, Ingrid Seward, who has written more than 20 books about the Royal Family, takes a deep dive into the Queen's 70-year marriage and the rumour that's plagued it: Philip's fidelity.

My Husband And I: The Inside Story Of 70 Years Of Royal Marriage analyses how Elizabeth, 92, and Philip, 97 have endured and enjoyed an almost century-long union.

The book revives the lingering allegations of Philip's affairs, his ties to numerous women included stage actress Pat Kirkwood during the 1940s.

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Previous reports claim the Duke and Kirkwood had a total of seven meetings, beginning with Philip visiting the actress in her dressing room before a show.

The initial meeting allegedly led to dinner and all-night dancing, while a young Elizabeth was at home, eight-months pregnant with Charles.

The Mirror has reported that Kirkwood always denied accusations of an illicit relationship with Philip, right up until her death in 2007.

Of her investigations, Seward told Fox News: "... I never got a conclusive answer. There's so much gossip about Philip and his affairs, but all the women that deny it, that have been picked out of possibilities of having affairs — well, most of them are dead now. … And Philip himself obviously denies it."

Claims of concrete evidence did come in 2012, when The Telegraph reported that royal biographer Michael Thornton had possession of letters written between the Duke and Kirkwood.

According to Thornton, he was under strict instruction not to show the details of the letters to anyone "except the person who will be chosen as Philip's official biographer after his death".

He also said Kirkwood had been upset that Philip had never officially denied the rumour, which could have done much for her reputation.

The Telegraph also noted, however, that nothing untoward occurred between "the Prince and the showgirl".

Beyond Kirkwood, the Duke has also been linked to actress Helene Corder. While Philip is the godfather to Corder's two children, People magazine has previously claimed he in fact fathered them. But Corder said the allegation was "ridiculous" and pointed to a French fighter pilot as their biological dad.

Two other actors, Anna Massey and Merle Oberon have also been rumoured to be linked to Philip.

And in the Netflix series, The Crown, it is suggested that the Duke was involved with a Russian ballerina in the 1950s. In reality, no evidence has been found to support this.

But from Seward's research, she has concluded: "No one is saying anything (about these stories) and probably won't until after the Queen dies.

"No one will say anything because anything would be very hurtful to her if indeed they were true. But, there are lots of stories. You can't ignore it."