Antin said he was surprised to see the new mother and daughter, who have returned home now with boyfriend Kanye and mother Kris Jenner, reported Daily Mirror.
"When I walked in to see her, Kim was holding the baby. I said, Oh my God. You're a natural.' Kim said, 'I know - it's so weird!," she said.
The Pussycat Dolls founder said that Kardashian and baby both are doing well.
"The baby is beautiful. Kim keeps telling me how much fun it is to be a mom. She and Kanye are so happy," he added.