The musician's 21-year-old granddaughter Assisi is expecting a baby with her chef boyfriend, and the new addition to the family will make the 70-year-old star a first-time great-grandfather, according to Britain's Daily Mirror.
Socialite Assisi is the eldest child of Jagger's daughter Jade.
A source tells the newspaper, "She (Assisi) and (her partner) Alex are thrilled and broke the news to their immediate families last week. Jade was a little taken aback at first, not least because it means she will be a grandmother by the age of 42... Mick is delighted and has no qualms about being a great-grandfather. He's been joking about becoming a great, great, granddad and still performing!"