Jason Biggs is to become a dad for the first time.

The 'American Pie' actor and his wife, Jenny Mollen - who wed in 2008, shortly after meeting on the set of rom-com 'My Best Friend's Girl' - announced they are expecting their first child together.

The funnyman broke the news during his appearance on US show 'Chelsea Lately' yesterday (17.07.13).

Host Chelsea Handler commented on a picture of Jenny, saying: ''Her breasts look really engorged.''

Jason quipped: ''Her breasts are very big these days. Would you like to know why? Cause I put a baby in her belly!''

Jenny, 34, confirmed her pregnancy by posting a picture of her sonogram on Instagram, jokingly writing, ''My new assistant is so f***ing lazy!''

She then shared an image of four different pregnancy tests she had taken - which all showed positive.

Jason took to Twitter after his TV appearance to spread the word, joking he hoped the announcement hadn't spoiled the impending arrival of the British royal baby for Prince William and Duchess Catherine.

The 35-year-old actor wrote: ''My wife @jennyandteets is pregnant. My sincerest apologies to Kate Middleton for stealing all of her thunder. #AmericasBaby''.

Fans and friends were quick to congratulate the star on his big news, with one posting on Twitter: ''Yayyy! the REAL royal baby!''

The couple had said they were trying to start a family earlier this year after five years of marriage.

Jason said: ''We're right in that zone. That's our next step.We figure we've been married five years next week, so we figure now it's about that time. I'm ready!''