Christian Siriano knows he's the right choice to be a mentor on Project Runway.
"I really think that a mentor in this type of role, or in this business in general, needs to be a designer," Siriano explained to ET's Marisa Runyon. "It's kind of impossible to kind of give advice without actually knowing what goes on really in the business."
The 33-year-old designer, who was the winning contestant of season four, is having a full circle moment as he replaces Tim Gunn as mentor in the revamped season that returns to its original network, Bravo. It introduces a new lineup of judges, including supermodel Karlie Kloss, who takes on role of host from Heidi Klum, designer Brandon Maxwell and journalist Elaine Welteroth. ELLE editor-in-chief Nina Garcia also returns as a judge for the series' new run.
Following his win in 2008, Siriano has established himself as an A-list designer, dressing some of Hollywood's biggest stars, such as Cardi B, Emily Blunt, Lady Gaga, Sarah Jessica Parker, Christina Hendricks, Angela Bassett, Ashley Graham and Michelle Obama.
He brings his wealth of knowledge and experience to the table as he guides the new contestants on their design competition journey.
"It was such a fun experience to get to help this young, new generation, and I think fashion is so, so different fro when I was on the show. I think about that a lot, because I'm like, oh my gosh there was no Instagram when I was on the show. It's wild! So many things are so different. I'm glad I'm able to be there and hopefully guide them, 'cause it is a new world."
Though he's all about giving guidance, Siriano is not holding back when a contestant needs a wake-up call.
"Obviously, I did the show, so that's one thing. And it's also 'cause I've dressed a million people on the carpet, [and] had so many collections. So I'm definitely, I think I'm like, 'That fabric's not going to work,' and I'm not telling them because I'm being harsh. I'm being like, it just won't. I kind of know and hopefully that kind of helps them a little bit."
Fabric choice is crucial to create a beautiful garment and no one emphasizes that more than Siriano.
"You forget that like, you don't have a lot of time, so they're picking satin and tulles and fabrics that are so hard to make, so that was driving me crazy the whole first couple challenges. I was like, get a backup fabric 'cause I beg you. And every time the backup fabric was used."
Project Runway premieres tonight at 8 p.m. ET/PT on Bravo.