Duvall, who was a billed guest on the show, brought out his prankster pal and asked Kimmel to present a photo of the two men baring their backsides to the host's friend Howard Stern as a belated 60th birthday gift.
The Godfather star then set MCConaughey up for a great joke as Rooster crowed about his little brother's Oscar win earlier this month (Mar14).
Duvall said, "I've got an Oscar too," prompting MCConaughey to respond, "Yeah, but his fans are still alive!"
Rooster then explained that he and Duvall have become great friends over the years, adding the two men have a lot in common.
He explained, "We both actually have younger wives and both of them are named Luciana. Mine's young enough to be my daughter, his is young enough to be his granddaughter!"
Duvall chuckled and recalled a magical moment while he was courting actress/director Luciana Pedraza: "She said, very romantically when we first met, 'I wonder what it's gonna be like when we grow old together', and I said, 'I already am old!'"
The 83 year old's fourth wife is 41 years younger than him. The couple wed in 2004.