Tarek and Heather Rae El Moussa Are Having a Baby: 'We Weren't Expecting This!'

Tarek and Heather Rae El Moussa are expecting their first baby together!

The couple were in the middle of in vitro fertilization treatments and had even scheduled a date to transfer an embryo next fall when they got a happy surprise a few weeks ago, they tell PEOPLE exclusively.

"It was a huge shock," says Heather, 34. "We just weren't expecting this. We had just gone through IVF. We had embryos on ice. We had a plan." But after the disbelief wore off, the Selling Sunset star was elated. "I think when you least expect it and there's no stress in your life, the world just brought us what was meant to be. I'm so excited that it happened like this."

Having a baby of their own wasn't always in the game plan for the pair, who got together in 2019 and tied the knot last fall. Tarek already shares kids Taylor, 11 and Brayden, 6, with ex Christina Hall, and Heather felt fulfilled being what she dubbed "a bonus mom."

"When we first started dating three years ago, we went into our relationship not planning on having children together. I really love being a bonus mom to Taylor and Brayden. They're such incredible kids and I love them so much," she says. "But as your love grows more and more and you fall deeper in love with someone and you build this life together, I started picturing myself having a child with Tarek. I started thinking I just wanted to create something with the man that I'm in love with."

"I'm just obsessed with my kids. They're my everything, so having another one is just icing on the cake. I'm so excited," says Tarek, 40.

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Adds Heather, "He's such a good dad. That was another reason why I wanted to create something with him. Seeing him with Taylor and Braden, he's just so obsessed with them. And he's such a doting, amazing dad. I can't wait to see him with our baby."

The pair, who are in the middle of filming their new HGTV docu-series The Flipping El Moussas, got the happy news a few weeks ago and are due early next year.

The day they found out Tarek was sitting on a Zoom meeting and says, "I just had this weird feeling, and I was like, she needs to take a pregnancy test right away." Heather said OK and Tarek "went back to work and completely forgot about it."

Heather took two tests. "Both came out 'undetected,'" she recalls. "I said, 'Oh, I must have done it wrong.'" Tarek left for a job, and then things took a turn at home.

She took one more test. "I was organizing my clothes. I was just doing other things, and probably like 20 minutes later I was like, 'Oh, the pregnancy test.' I went and looked and it said full-on pregnant." She screamed, startling her assistant, who burst into happy tears when Heather shared the news.

"I took two more tests. Right away, [they said] pregnant," she says.

She surprised Tarek later that day when he returned from work, hiding the tests in a gift box with confetti and a baby onesie. "I was like, I have to tell him in a cute way. I can't just text him," she jokes.

"I'm opening up this box and there are these sticks. I'm staring at them and thinking, are these COVID tests? And then I said, 'Oh, s---! Are you pregnant?' She said yes, and that's how we found out."

"I swear, it was 30 seconds of him trying to put it together," she recalls with a laugh. After she confirmed, "I started tearing up because it was such a moment of excitement and relief. He was so happy. We hugged and embraced each other and kissed."

The couple has already done the test to find out the sex of the baby, but will be surprised by the results at a reveal party in a few weeks.

"Tarek thinks it's a girl. I don't know yet. I just want a happy, healthy baby," says Heather. "We already have Tay and Bray, so I'd be happy with either. But I secretly want a little mini Heather."

She's also shared the happy news with a few of her Selling Sunset co-stars: Mary Fitzgerald, Chrishell Stause and Emma Hernan. They're "so happy," she says.

And the unexpected timing couldn't be better.

"My sister is pregnant with her third baby," says Heather. "It was my parents' dream that we were pregnant at the same time. I never thought that would happen and the fact that it happened on its own just makes this so special for our family."

Expanding their family does mean one more big change for the pair: finding a new home. The real estate pros just finished a massive renovation on their property in Newport Beach, Calif. but will now look for something even more kid-friendly.

"We are looking for a new house and if we don't find that house when the baby comes, we do have room for the baby at our current home," says Tarek. "But we definitely need to find a bigger house with a yard and some more space."