"I don't know why, they've never watched Sesame Street ever, but they both love Grover. So, I do an impression of Grover for them," he told host James Corden. "It's relatively simple."
The former That's '70s Show star then stood up to perform his Grover impression, with both Corden and fellow guest Sean "Diddy" Combs watching eagerly.
"Hello, my name is Grover, and today we are going to learn two things: far and near," Kutcher exclaimed in a pitch perfect impersonation of Sesame Street's beloved blue character.
While on the show, Kutcher also participated in Corden's popular Drop the Mic segment and Diddy served as judge.
"I heard I was battling an A-list hunk, but when I saw Ashton Kutcher I knew I was getting Punk'd," Corden began his rap. "You haven't had a hit movie since 2002. You were so bad in Jobs even Siri won't talk to you."
The Ranchstar didn't hold back when it was his turn.
"My careers been doing fine ever since the '70s, your career's an Uber driver for real celebrities. You were at the royal wedding and that seems right, every wedding has a guest they didn't invite," Kutcher volleyed back. "People see me at valet they say, 'Look there's a star.' People see you at valet they say, 'Dude, Where's My Car?'"
Diddy, 48, ended up crowning Corden the winner, making Kutcher the first guest in the show's history to lose — perhaps thanks to one of Corden's best insults.
"Valentine's Day and New Year's Eve are movies you fumbled. You've ruined more holidays than a Trump-loving uncle," the 39-year-old host rapped.
Prior to losing on Late Late Show, Kutcher recently appeared on Conan and revealed he's losing something else: his hair. Here's more on that story: