ET caught up with a few of Duff's cast mates at a fan screening in New York on Monday, and they dished on the actress' pregnancy journey.
ET's Keltie Knight caught up with the expectant mom's co-stars before a fan screening of Younger at the 92nd Street Y in New York City on Monday, and while Duff herself wasn't able to attend, her fellow cast mates were effusive in their excitement and gave ET an update on how he's been holding up while pregnant with her second child.
"She's doing great!" Foster marveled. "I just saw her in L.A. we had a summer party and she came over and she seemed so happy and I'm so excited for her."
According to Foster, Duff sprung the news on them midway through production on the show's fifth season.
"We all have kids, and we're all like sharing cute videos of [them]… and she was like, 'Well, I have a video,' and she shows us a sonogram! And we're all like, 'What?!,'" she shared.
"She actually introduced me to some of our favorite onesies which she bought us," said Foster, who shares her daughter, Emily, with husband Ted Griffin. "She sent a big care package right after Emily was born."
However, Foster said she's excited to return the favor, sharing, "I'll be able to help her [now] because she'll have newborn, a baby girl."
"But we all sort of share advice and talk about our kids a lot on the set," Foster added.
Duff first revealed that she and her boyfriend, singer Matthew Koma, are expecting their first child together back on June 8, posting a photo of Koma with his arm around her shoulder kissing her head, and the curve of her small baby bump visible under her sleeveless summer dress.
"Guess what guys! @matthewkoma and I made a little princess of our own and we couldn’t be more excited!!!!!!" Duff wrote. Later in the month, Duff shared a video of her gender reveal party, which is when she first told fans she was expecting a baby girl.
Younger star Nico Tortorella also joked with ET on Monday about how Duff "pulled a fast one on everyone" by keeping her pregnancy under wraps throughout production.
"She is such an incredible mom and I got to spend some time with Luca on set this year and he’s just such an incredible kid," Tortorella, 29, told ET's Leanne Aguilera at the ATX Television Festival in Austin, Texas, in June.
"She's been talking about having another baby for years and I’m so excited that she gets to have one."
Check out the video below to hear more.
Younger airs Tuesdays at 10 p.m. ET/PT on TV Land.