Tina Fey breaks down how she cast the new 'Mean Girls' actors

As well as writing and starring in the new Mean Girls movie, Tina Fey was also heavily involved in the casting — and in the Tonight Show clip above, she tells Jimmy Fallon some roles were easier than others.

Fey says they knew they wanted Renée Rapp to reprise her Broadway role as Regina, and wanted to cast Avantika as Karen ("She's so gorgeous it's like, stupid," says Fey) — but Gretchen took a lot longer.

"I had one day where I was like, 'I'm going to go back and watch every single tape of every Gretchen that's come in," Fey explains. "So I spent a whole day watching all of them, and then I was like, 'This girl, I love this girl, Bebe Wood, she's perfect, she's Gretchen!' We hired her and then we went to look at her IMDb page, and then I realised that I had worked with her when she was 10 on 30 Rock."

On casting Christopher Briney as hearthrob Aaron, meanwhile, Fey explains that she herself can't process him that way — so she casually FaceTimed a group of her daughter's friends during a Zoom callback with Briney to get their approval.

Mean Girls opens in theaters Jan. 12.