The Anger Management star, 47, confirmed the happy news himself during an appearance on The Late Show With David Letterman Monday, Jan. 14. He told Letterman he was excited about the new addition to his family, but he also admitted to being a little nervous.
"Me as a grandfather, Dave...I don't know. It's like the world's going to crack in half," he joked. "It's fabulous. It's just not a title I'm ready to adopt."
Asked whether he thought he'd be a good grandpa, the actor quipped, "Well, yeah, because you can leave the kid!"
Shortly after the interview, Sheen's ex-wife Denise Richards posted the news on Twitter. "I guess some of you have heard...Charlie Sheen is going to be a Grampa...yes, GRAMPA!" she wrote. "His beautiful daughter Cassandra is gonna be a mama."
Cassandra is Sheen's daughter with his high school sweetheart Paula Speert. The actor also has two younger daughters, Sam, 8, and Lola, 7, with second wife Richards, and 3-year-old twin sons, Bob and Max, with third wife Brooke Mueller.