Sir Mick Jagger's pregnant granddaughter says her family are very fertile.

Jade Jagger's 21-year-old daughter Assisi is expecting her first child with her chef boyfriend of three years, Alex Key, in April and she admits the women in her family do tend to get pregnant quickly.

She said: ''I wasn't trying, but I think at my age you don't have to really try. The women in our family just tend to have children young, it runs in the genes.

''I grew up quite quickly and wouldn't have considered having a child if I was doing what my friends are doing at this stage, messing around. I don't drink, I don't smoke, and I'm very settled.''

Assisi credits her boyfriend with helping her to grow up and insists they will be good parents and don't find the concept too daunting, despite still being in their early 20s.

She told HELLO! magazine: ''We're very good at looking after ourselves, which means we'll be able to look after somebody else.''

The youngster's mother Jade - who gave birth to her when she was 19 - insists she isn't struggling with the concept of becoming a grandmother at 42, although she was worried her rock legend father, who has seven child, might find being a great-grandfather ''traumatising''.