No joke: Jim Carrey's going to be a grandpa.

A rep for the 47-year-old actor tells that his daughter Jane, 21, is expecting her first child with Alex Santana, who is in the band "Blood Money" and goes by the stage name is "Nitro."

"I'm very excited," Carrey tells Us. "Jane is going to be a great mom."

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Carrey had Jane with ex Melissa Womer.

He has been dating Jenny McCarthy for more than four years. She has a son, Evan, 6, who battled autism.

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Last year, Carrey said they have no plans to wed.

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"I love Jenny very much, and we have a great relationship. And we've both been married a couple times," he told Larry King. "I like it the way it is, and I think she likes it the way it is."