The 34-year-old mother of three caught up with ET at the Baby2Baby 10-Year Gala presented by Paul Mitchell over the weekend where she couldn't help but gush over the 65-year-old Sex and the City alum.
"I've been to work every single day for the past, like, 11 weeks, and the day that she shot was my day off, and I was like, 'I'm coming to work.' Like, what the hell, don't leave me out of this one 'cause we're not actually shooting together," Duff explained of Cattrall's time on set. "She plays all the flash forwards, and she's just incredible -- like, really incredible. She speaks and you're just like, 'I'm listening.'"
Duff was thrilled to be working with the actress, adding, "She's just a force, but she's so kind. She's so warm, and I'm so excited to have her on board, truly. It's a really cool show, and I'm really proud of it and happy to have someone like her stepping on in."
As for the comparisons between the two TV stars, Duff said she sees the resemblance.
"Honestly, we kind of look alike," she admitted. "I never realized it, but when we were sitting there, I was like, 'I can see this, and God, I hope I look like you!'"
How I Met Your Father is set to premiere in 2022 on Hulu.
As for the Baby2Baby event itself, Duff said she was very passionate about Baby2Baby's cause, which is providing resources to all mothers.
"I really can't even fathom what that would be like to be put in a position where you can't necessarily give your babies the things that they need like diapers or formula or supplies," she told ET. "It's incredible the work that they do."