|Sheen in "Two and a Half Men"|
Charlie's second ex-wife Denise Richards broke the news on Twitter, posting: "I guess some of you have heard ... @charliesheen is going to be a Grampa ... yes GRAMPA! his beautiful daughter Cassandra is gonna be a mama. (sic)"
'The World Is Not Enough' actress was married to Hollywood star Charlie from 2002 to 2006 and the pair have two children together, Sam, eight, and Lola, seven.
The actor - who is currently living with 24-year-old porn star Georgia Jones - is notorious for his tumultuous love life and hellraising antics and has five children with three different women.
Fans took to the social networking site to congratulate Charlie on the big news, with JayLink _ writing: "Welcome to my world Charlie Being a Grand Father is awesome!! (sic)".
@Team_Giudice added: "WOW! Good luck to Cassandra! May the baby be full of joy, love, giggles, and smiles. Congrats! (sic)"
Brooke is likely to be heavily involved in the baby's life as she regularly looks after the youngest members of Charlie's brood, three-year-old twins Bob and Max. The model recently cared for them in December when his troubled third ex-wife Brooke Mueller headed to rehab again.
She commented: "This is not the first time I've had all five, they're Sam and Lola's brothers. It was a full house, lots of love and life. Brooke knows anytime, and Charlie, that any time they need help with the boys, that I'm there.
"I know it doesn't seem normal, but it is our normal. They're little kids and I love children, and like I said, it's our daughter's brothers, so I can't say no."