Prince Charles had a decades-long “infatuation” with Barbra Streisand — and became so close to the star that Princess Diana “would not have been surprised if they had an affair,” a royal pal has divulged.

Charles and Streisand first met back in 1974, when the prince was a 26-year-old officer docked in LA and given his choice of any Hollywood star to meet, according to a new book by Christopher Andersen.

Prince Charles had seen the 1968 Streisand movie “Funny Girl” three times and had kept a framed photo of Streisand on his wall at Cambridge and in his private quarters in Buckingham Palace. He’d even confided to his personal valet of his choice to meet Streisand, “I’m sure they thought I’d say Raquel Welch . . . Streisand is my only pinup,” “Game of Crowns,” out Tuesday from Simon & Schuster, reports.

But Streisand seemed “nervous” and “tight-lipped” during the ’74 encounter, later joking of the meeting, “Who knows? If I’d been nicer to him, I might have been the first real Jewish princess.”

She had another chance when she saw the royal at a ’94 LA gala. According to British author Harold Brooks-Baker, the pair “had a secret rendezvous at his suite in the secluded Bel-Air Hotel” — officially booked as a “private tea.”

At another event 10 months later in London, a source recalled, “The prince and Miss 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.

According to Diana confidante Lady Elsa Bowker, the princess had even said “she would not have been surprised if they had an affair.” But Charles was already involved with Camilla Parker
Bowles at the time — whom Bowker also added would have been “absolutely thrilled” about Charles spending time with Streisand. “That would have excited her.”

A rep for Streisand didn’t immediately comment.

This story first appeared in the NY Post.