Mick and Melanie first started dating in 2014.
A spokesperson for Mick confirmed the news and said:
"This is great news. It will be Mick's eighth child and nothing fazes him. He's been incredibly supportive.
"She's very bright, intelligent, sparky and has her own ideas about how she wants to lead her life. She knows what a great relationship Mick has with all of his children and can't wait for him to be a dad again. "They are taking the news in their stride."
However, Melanie who is from Connecticut in the US , reportedly won't be moving to London to live with Mick when the baby is born, although sources say "he will love and support this child".
Instead she is believed to be planning to move to either Los Angeles, where he spends a great deal of time, or back home to Connecticut to be near her family.
Jagger has seven children with four different women. Melanie Hamrick will be the 5th woman and this will be his eighth child but Melanie's first.
Source: The Sun.