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

Although they were in the middle of IVF treatments, with an embryo already scheduled to be transferred, their happy surprise gave them both quite a shock a few weeks ago.

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In an exclusive with PEOPLE, Heather says, "It was a huge shock. We just weren't expecting this. We had just gone through IVF. We had embryos on ice. We had a plan." Once they processed what was happening, they were both over the moon. "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."

Heather, a "Selling Sunset" realtor, 34, and Tarek, 40, a HGTV star, married in 2021. The couple didn't always plan to have a baby together. Heather says being a "bonus mom" to Tarek's kids is fulfilling all on its own.

Tarek shares two kids, Taylor, 11, and Brayden, 6, with ex-wife Christina Hall.

Heather says, "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. "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."

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"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," Heather adds.

Heather and Tarek are busy filming their new HGTV docu-series "The Flipping El Moussas." And their new bundle of joy is set to arrive early next year.

As for how they found out, Tarek says, "I just had this weird feeling, and I was like, she needs to take a pregnancy test right away." Heather said OK but then Tarek, who got busy with work, went on with his day and promptly forgot all about it.

Heather says she took multiple tests. The first two came out "undetected."

Related: What does a faint line mean on your pregnancy test?

When she took the third test she got busy doing other things, she describes. "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." Heather gave a full-on scream (who wouldn't!) scaring her assistant who then burst into happy tears from the good news.

She says she took two more tests before preparing how she would tell her husband.

When Tarek got home from work that day, Heather handed him a box filled with the tests, a baby onesie, and lots of confetti.

"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."

Then, of course, there were more happy tears, kisses and hugs.

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The couple have already had an appointment to determine the sex of their baby but they're waiting for their gender reveal party to be surprised with the results.

"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 says she's already shared her news with her "Selling Sunset" costars who are overjoyed for her.

Related: ‘Selling Sunset’ star Christine Quinn says she had PPD while filming

If the happy news couldn't get even better, Heather shares that her parents always wished that she and her sister would be pregnant at the same time. And guess who else is pregnant right now? That's right, Heather's sister!

"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."

Heather and Tarek also shared that they are hoping to find a new home before the baby arrives. They just finished a renovating their property in Newport Beach, California but say they need more space as their family expands.

"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."

Congratulations to the El Moussas!