Pete Wentz loves watching his girlfriend handle his baby son.

The Fall Out Boy rocker, 35, and his beau Meagan Camper welcomed their first child into the world two weeks ago and the hunk has praised his lover for the way she's adapted to motherhood so quickly.

He told ''Meagan is a natural mum and it's amazing to watch her with him.''

The couple named the tot Saint Lazslo because they felt blessed that he had waited until Pete had finished touring with his band before making his entrance into the world and thought he deserved a holy moniker.

The hunk, who assisted in the delivery of the little one, explained: ''I think at some point, the name Saint came up because we thought he'd be a saint if he waited to arrive until his dad was home from tour, and he did. The name suits him.''

Meanwhile, Pete's five-year-old son Bronx Mowgli, with whom he has with his ex-wife Ashlee Simpson, has fallen in love with his baby half-brother and is already planning for the future with the new addition involved.

Pete joked: ''Bronx is already planning everyone's Halloween costume.''

Pete and Meagan, who have been dating since September 2011, announced they were expecting a baby together in February when they posted a picture on Instagram of them kissing.

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