Peta Murgatroyd Reveals Why She Couldn't Keep Her Pregnancy a Secret from Dancing with the Stars Partner Nyle DiMarco

"I had to make sure my costumes were hiding it as much as possible, but a couple of people noticed," says the pro dancer

Season 22 of Dancing with the Stars wasn’t easy for Peta Murgatroyd, but that had nothing to do with her partner Nyle DiMarco.

“I was so sick,” Murgatroyd says in the current issue of PEOPLE. “Nyle would see me falling asleep on the couches and on the floor of the rehearsal studio. He’d look at me like, ‘What’s going on?’ And I’d go, ‘Oh, I’m just tired.’ ”

But in reality the pro dancer, 29, was suffering from nausea, a side effect of being pregnant with her first child with fiancé Maksim Chmerkovskiy, 36.

Murgatroyd had planned on keeping her pregnancy a secret until she entered her second trimester. But since she’d become pregnant just a few months into the season, it was impossible to hide by the May 23 finale.

“I had to make sure my costumes were hiding it as much as possible, but a couple of people noticed,” says Murgatroyd, who went on to win the season with DiMarco.

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In fact, DiMarco had known for weeks before he mentioned it during semi-finals week in mid-May.

“Nyle actually came up to me and wrote me a text that said, ‘I know,’ ” Murgatroyd, who is now in her second trimester and currently enjoying life on the road with Chmerkovskiy as he and his brother Valentin travel the country in Maks & Val: Live on Tour. “I just lost it laughing because he had known for about two weeks and didn’t say anything to me.”

But just because the happy couple were keeping the news private doesn’t mean they were keeping it completely quiet.

“The first people we told were our parents. We skyped them and they were all extraordinarily elated,” says Murgatroyd, who is due in January and is planning her wedding to Chmerkovskiy for next summer.

“They have been waiting for this for so long. My parents have wanted me to be pregnant for so long and Maks has been wanting a baby for a long time. I can’t wait to be a mom!”

For more on Chmerkovskiy and Murgatroyd’s happy news, pick up the latest issue of PEOPLE, on newsstands Friday.

— Patrick Gomez