Paul Newman’s celebrated 50-year marriage to Joanne Woodward wasn’t as solid as it appeared, says a new biography arriving seven months after the actor’s death.

Paul Newman: A Life, by Shawn Levy, says journalist Nancy Bacon had a year-and-a-half affair with Newman after meeting him on the set of “Butch Cassidy and the Sundance Kid” (1969). Bacon has been claiming the liaison since the 1970s, when less attention was paid to celebrities’ personal lives.

Though he never confirmed the affair, Newman was candid about his difficult but rewarding marriage, famously saying, “I have steak at home, why go out for hamburger?”

Bacon broke off the romance, Levy writes. “I finally said to myself: ‘I can do better than this,’ ” he quotes her as saying. “I told him: ‘You’re always drunk and you can’t even make love.’ ”

The book (out May 5) calls Newman a “functioning alcoholic” who drank a case or more of beer each day “followed by the hard stuff, usually Scotch.”