ET joined the HGTV star at her boho-style baby shower on Sunday.
Tarek El Moussa got a heads up about his ex's new pregnancy.
ET's Lauren Zima spoke with Christina Anstead at her baby shower at Balboa Bay Resort in Newport Beach, California, on Sunday, where she revealed that she gave her ex-husband a courtesy call that she was expecting a baby with her new husband, Ant Anstead.
"I told him right before I told the kids," shared Christina, who filed for divorce from Tarek in 2017 but still works with him on their HGTV show, Flip or Flop. "I waited after the first trimester to tell them to make sure everything was OK."
The conversation between the exes was "good," the designer expressed, adding that she and Tarek have moved past the awkwardness of working together after their breakup. "[We've] just been doing it for a few years now, and it's sort of normal, I guess," she said.
Christina -- who shares daughter Taylor and son Brayden with Tarek -- also became stepmom to Ant's two kids, daughter Amelie and son Archie, after she and Ant tied the knot last December. She found out she was pregnant soon afterward.
"It was immediate, that connection [with Ant]. I knew the second we drove to dinner together, we just had that spark, but [we're] also so comfortable together. [We feel like] we've known each other forever," Christina expressed.
"[Having kids] wasn't on our mind -- if it happened, it happened. It definitely was not something where [we said], 'We want a baby right now,'" she recalled. "It happened quickly. We got back from our honeymoon [and] found out I was pregnant."
"I felt off during the honeymoon and when I got home, I felt I should take a test, not thinking at all it was going to show positive," Christina explained. "I was just like, 'OK, this makes five -- here we go!'"
Ant was "shocked" but excited about becoming a dad again, and both his and Christina's kids are offering name suggestions for their little brother, though she jokes most of their recommendations are the names of "kids at school they like."
"We have not chosen [a name] yet. We have a few up in the air. Between the four kids and us, this is still a process," she shared. "We are going to wait until right before and make a decision."
"The kids are such different ages, but they get along so well. It's been super fun traveling and spending time together and we are looking forward to welcoming this new baby," Christina added.
Christina is due in September, and was 30 weeks pregnant at the time of her baby shower on Sunday. "My good friend Cassie put this all together and it's the first time i'm seeing it, it's so cute. It's a nice boho vibe and kind of goes with my house and the nursery style that we are doing," she noted. "She did such a great job, and it's just really close girlfriends and family. It's going to be a nice day."
Between her kids and two TV shows -- Christina on the Coast is currently airing, while Flip or Flop returns in August -- the HGTV star hasn't started putting together her nursery yet.
"I've been ordering things and there's pieces that are arriving, but it is not put together. It is still currently in the guest room, so we have about 10 weeks to get it all organized," she said.
"My house is a chic boho vibe, so we're going with a lot of layered rugs and dream catchers, like what you see around here. I'll probably be utilizing things that Cassie made, just a lot of greenery and plants and softened it up with some cute stuffed animals," Christina continued.
Fans will see the nursery come together on TV -- but cameras won't be following Christina into the delivery room. "[It's] not that kind of show. No, thank you," she cracked, revealing that Ant will be by her side, and "that's it."
See more on Christina in the video below.