Pete Wentz wants the sex of his unborn child to be a ''surprise'' until the birth.

The Fall Out Boy bass player and his girlfriend Meagan Camper are set to welcome their first child into the world later this year, but they've decided not to find out whether they're expecting a boy or girl until the tot arrives.

Speaking to E! News, he said: ''I don't know yet [whether the baby is a boy or a girl], [but] I think we'll probably do a surprise on this one.''

Pete - who already has five-year-old son Bronx Mowgli with his ex-wife Ashlee Simpson - is looking forward to meeting his new bundle of joy in coming months.

He explained: ''What's more exciting than having the little pitter patter of having another little gremlin running around and now it will be two-on-two.''

The 34-year-old star and his model beau announced their baby news in February by posting a picture on Instagram of them kissing and Pete touching Meagan's stomach.

He accompanied the snap with the caption: ''We're super excited to announce we're expecting a baby!''

The couple, who began dating in September 2011, have been hoping to start a family for a while.

A source said previously: ''They've been planning on this for a while. And they're really excited for Bronx to have a new little buddy.

''Meagan is a big sister and has a great relationship with Bronx. She's naturally maternal so this is perfect.''