"She's adorable – could be one of the cutest babies I've ever seen," he told AM Network. "And I'm not just saying that. She really is just a stunner."
He added that new mum Kim was "doing amazing".
PR manager Jonathan, who makes frequent appearances on Kim's reality TV show Keeping Up With The Kardashians, loves spending time with North but said he refuses to change her nappies.
"No, no diapers," he laughed. "I'll babysit but no diapers… I don't do diapers, I don't do dishes and I don't cook."
Kim's mum Kris Jenner recently teased fans by hinting that her daughter Kim Kardashian's baby North West might appear on the premiere of her chat show on Monday night.
The mum-of-six posted a photo on her Twitter and Facebook pages of her on set holding a baby accompanied by the caption, "You never know who will stop by our show today!"
But fans were left disappointed when it was revealed that the snap was a hoax. Instead of baby North, whose nickname is Nori, viewers were treated to appearances from Khloe Kardashian and Kourtney Kardashian.
Kris refuses to confirm or deny whether her granddaughter will appear on the show. There are still four episodes to go in which Kim might introduce her to the world.
"I think you're just going to have to wait and see and tune in because I am not sure if that is going to happen," said Kris to host Matt Lauer on The Today Show, when asked if North would appear on her grandmother's talk show.
"I won't tell you it won’t happen," said the Kardashian family matriarch, laughing and holding her ground. "Give you a little something to think about. You never know who is going to show up."
Kris, who manages the Kardashian sisters, said, "I think everybody, depending on what's going on in their universe, will come on and pay a little visit here and there.
"That's just the natural order of things in my house. It's like, 'OK, mom's got a new project'" to support."