The actor, who starred in and directed the hit 2001 movie, recently announced plans to bring Zoolander back to the big screen nearly a decade after the first film hit cinemas.
Stiller has been keen to make a follow-up for the "last six or seven years" but admits he found it difficult to contemplate work on a sequel after his screenwriter pal Drake Sather, the scribe who created the title character, committed suicide in 2004.
He tells Parade magazine, "We've been working on it on and off over the last six or seven years. The biggest hurdle for me personally was that Drake Sather, who created the character, passed away. He was a good friend and the lump for me was it's hard to imagine doing it without him.
"Now my buddy, Justin Theroux, has committed to directing and writing it. So I'm excited and I think it's going to happen. I want to be able to do something that lives up to the first one. That's the challenge."