Drivetime DJ James had previously been tipped to replace Moyles, but he insisted to Digital Spy that he wasn't disappointed not to land the gig.
"I wasn't disappointed, but I love the fact people thought that I was going to get it. That was just the product of me getting promoted to drivetime, which is the second-biggest show and people often describing it as a 'stepping stone' to the breakfast show," said James.
"I never really thought of it like that and it was only people tipping me for it and going, 'Do you want to do it?'
"Well, I'm not going to say no, but I didn't want to do it because I was really happy doing my show."
Commenting on early criticism of Grimshaw's performances from some listeners, James said: "The beauty about radio is that it is so personal and it's great that people have opinions. Otherwise you're just wallpaper. I think it's really healthy to have that.
"I've got people that I hate and people that I love on the radio and it's not a personal thing, it's just they're right in your ears and you have to get on with this person, do you know what I mean? It's a bloody hard job and Nick's doing such a good job.
"The Radio 1 bosses have made a big statement with me on in the afternoon and Nick on at breakfast. They have changed a generation of Radio 1 listeners."
James and Russell Kane return for their second series of entertainment show Britain Unzipped tonight. Joking about his relationship with his co-star, the DJ said: "It's not a TV bromance, it's real baby.
"You can't fake that love. We're just really good mates. We went away to Ibiza together in the summer, we both went away for the Radio 1 weekend which was a messy affair."
The first episode tonight features an appearance from DJ Sara Cox and Olympic boxer Anthony Joshua, and James revealed that it would also include an embarrassing moment for a University of Newcastle student.
"We sent our cameras to his house without him knowing. We invited him down to the studio and he had no idea it was happening and we snooped around his house and we found some weird stuff in his bed," said James,
"His friends stitched him up properly!"
Britain Unzipped returns tonight at 10pm on BBC Three.