In a new interview with Barkers magazine, Mulligan calls those three months "awkward" and "horrible".
He says he constantly felt like a third wheel, but admitted his style of comedy didn't fit with the rest of the show.
"When you're doing something that clashes with the format of a show, it disappears. People don't actually register that it's going on. It just becomes invisible."
Mulligan goes on to detail how he wasn't invited to a photo shoot with Hosking and Street for Woman's Day, and says he was shuffled out of the studio to make room for guests during live broadcasts.
"It's around that point you realise you're probably not an integral part of a show ... it was a pretty horrible feeling."
Mulligan calls Hosking an "alpha nice guy" but couldn't understand the Newstalk ZB host's breakfast choice: Brazil nuts and a salad.
"There's nowhere to buy Mediterranean salad at seven in the morning, so he must be making it ... the night before," Mulligan quipped.
"That could be in any sort of state by the 7.30 morning news."
Mulligan, a food critic for the NZ Herald's Viva publication, had already revealed to the Herald that his departure felt humiliating.
"Wandering into an office of people - nice people- who regarded me with a mixture of awkwardness and pity, then having to front up on a show where, I suspect, the audience felt largely the same thing," he said.
"When I left I felt a bit humiliated and a little bitter, but those feelings didn't last long and didn't affect my life or mood in any real way."
Hosking and Street departed Seven Sharp last year with Hilary Barry and Jeremy Wells taking over.
Read more: Jesse Mulligan opens up about the dark days of Seven Sharp