While Hilary Duff only recently shared her big pregnancy news with the world, her Younger co-star, Nico Tortorella, has known for a while, and the actor says it's been difficult to keep quiet about it.

"I’ve known for a long time. It’s been really hard for me to keep it a secret," Tortorella, 29, told ET's Leanne Aguilera at the ATX Television Festival in Austin, Texas, on Saturday. "I’ve known for a few months."

Duff revealed on Friday that she and her boyfriend, singer Matthew Koma, are expecting their first child together. The 30-year-old actress is also the mother of a 6-year-old son, Luca, whom she shares with her ex-husband, retired NHL star Mike Comrie.

"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 marveled. "She's been talking about having another baby for years and I’m so excited that she gets to have one."

Tortorella -- who has been very open about his "ever-evolving" sexuality, self-identification as gender fluid, and recently married longtime partner Bethany Meyers -- said Duff's pregnancy is "so beautiful."

"It’s what we all are looking for in one way or another, and she's got it. She's preggers,"I love pregnancy so much. I have the fever so hard right now… I can't wait to start having kids. I’m so excited."

While Tortorella told ET that it was personally difficult to keep Duff's pregnancy under wraps, the show also had to come up with creative ways to hide her burgeoning baby bump while filming season five.

However, he said that the show's creator, Darren Star, didn't know "until after we wrapped, honestly."

"I think he was the last one to find out of all of us," Tortorella said, laughing. "[But] timing-wise, it’s perfect. She’s going to have the baby [and] we don’t start shooting until next year. It’s perfect!"

Duff took to Instagram on Friday to share the joyous news, 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.

Koma shared the same sweet snapshot to his own Instagram, writing, " We made a baby girl! She will be as beautiful and sweet as her mother... @hilaryduff another incredible chapter begins."

Check out the video below to hear more.

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