Asked how to pronounce the baby's name on 'Lorraine', he said: "Shut up, I don't know. I don't know, I haven't said it yet - I can't bring myself to say it.
"I wanted to call him Leonard - Leonard Cohen. 'Have you met my grandson Leonard Cohen?' But he's a fantastic little chap."
Bob - who also has daughters Fifi Trixibelle, 29, and Pixie, 21, with late ex-wife Paula Yates - is thrilled at how well Peaches and Tom have settled into family life.
He added: "He is cute and they're really good parents so it's great. They're really happy."
Bob is very happy that Peaches - who was previously married to Chester French drummer Max Drummey - has settled down with Tom - particularly because he likes the S.C.U.M. rocker's music.
Asked if he is happy Peaches is with Tom, he said: "I am, and he's a great guy, but importantly he's a fantastic musician - really, really good. I'm so thrilled that I can go to the gigs and not have to say, 'That was quite good,' I mean an amazing band. So it excites me actually, aside from the fact he's Astala's dad."