Speaking to Parade, the fashion consultant revealed that Klum's beau Seal often refers to him as the supermodel's "other husband".
"She's a dream. She's a doll," Gunn stated. "There's not a diva's bone in her entire body."
The TV personality also contended that Klum is very easy to work with during the production of Project Runway.
"It's just a huge gigantic joy and frankly a laugh-fest. She has a great sense of humour and we laugh all the time. It's joyous," he added.
Gunn joined Project Runway as a mentor to aspiring fashion designers during the show's first season.