Pete Wentz says his girlfriend Meagan Camper is "a natural" mother.
The couple welcomed their son, Saint Lazslo Wentz, into the world on August 20 and the Fall Out Boy rocker finds it compelling to watch her look after the tot.
Pete, who has son Bronx, five, with his ex-wife Ashlee Simpson, said: "Meagan is a natural mom. It's amazing to watch her with him."
The 35 year old musician has also explained why he and Meagan gave their son such an unusual name.
He told the new issue of PEOPLE magazine: "The name Saint came up because we thought he'd be a saint if he waited to arrive until his dad was home from touring. And he did! So it suits him."
Pete says Bronx loves his new baby brother and is already making plans to do fun things with his sibling.
When asked if his older son was showing any signs of jealousy, he said: "Not at all. Bronx is already planning everyone's Halloween costume!"
The 'Just One Yesterday' hitmaker split from Ashlee in 2011.
She recently re-married, tying the knot with Evan Ross - the son of Motown legend Diana Ross.
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