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, theSelling Sunsetstar 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.”

Christina Cernik

Tarek and Heather El Moussa

“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.”

Tarek and Heather El Moussa

“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.

Tarek and Heather El Moussa

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.

“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.”

Tarek and Heather El Moussa

She’s also shared the happy news with a few of herSelling Sunsetco-stars: Mary Fitzgerald, Chrishell Stause and Emma Hernan. They’re “so happy,” she says.

And the unexpected timing couldn’t be better.

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

source: people.com