Prince Charles may have cheated on Princess Diana with this major Hollywood star...

It's no secret that Prince Charles wasn't faithful in his marriage to Princess Diana. But, if rumours are to be believed, the Prince of Wales once had an affair with Barbra Streisand.

According to new book, 'Game of Crowns', out by royal biographer Christopher Andersen, Prince Charles had a decades-long “infatuation” with Barbra Streisand. The two were allegedly so close that a confidante of Princess Diana's said she “would not have been surprised if they had an affair.”

Charles and Streisand first met in 1974 after Charles was given his choice any Hollywood star he'd like to meet. He was 26 and a Naval officer docking in L.A. at the time. According to Andersen, there were different accounts of Charles meeting up with Striesand.

Prince Charles watched the 1968 Streisand movie 'Funny Girl' three times. He purportedly had photo of Streisand on his wall at Cambridge and in his private quarters in Buckingham Palace.

He even told his personal valet about wanting to meet Barbra. It was thought that Charles might wish to meet someone like Raquel Welch, but Streisand was his “only pinup.”

According to the book, Streisand was described as “nervous” and “tight-lipped” when she met the royal prince in 1974.

“Who knows? If I’d been nicer to him, I might have been the first real Jewish princess,” Streisand joked.

The two met again when they were at a 1994 gala in L.A. According to British author, Harold Brooks-Baker, Charles and Streisand “had a secret rendezvous at his suite in the secluded Bel-Air Hotel” — officially booked as a “private tea.”

Another source claimed that in London 10 moths later, Charles and Streisand “were very affectionate to one another.” And, “another housekeeper described Charles and Barbra as acting ‘quite flustered’ when she surprised them in Charles’ study,” the book claims.

Princess Diana's confidante, Lady Elsa Bowker, was the one who said that the princess wouldn't have been shocked if the two were having an affair. At the time, however, Charles was already having an affair with Camilla Parker-Bowles.

Ironically, Bowker added that Camilla would've been “absolutely thrilled” about Charles spending time with Streisand. “That would have excited her.”

Is there any veracity to this story? A rep for Barbra Striesand hasn't commented on the book's claims yet.