EXCLUSIVE

Richard Pryor had a lot of sex in the '70s -- and it was with both men and women -- including Marlon Brando ... according to Pryor's widow, Jennifer.

Jennifer confirmed the Richard-Marlon hookup, which Quincy Jones first mentioned in a pretty wild Vulture interview. As Q put it, Brando would "f*** anything. Anything! He'd f*** a mailbox. James Baldwin. Richard Pryor. Marvin Gaye." The allegation sent the Internet into a frenzy.

Jennifer tells TMZ ... Richard would have no shame about Quincy's comments. She says the comedic legend was always very open about his bisexuality with friends, and documented it extensively in diaries. Jennifer says she'll publish them later this year.

As for Richard hooking up with Brando -- she says, "It was the '70s! Drugs were still good, especially quaaludes. If you did enough cocaine, you'd f*** a radiator and send it flowers in the morning."