In an interview with PEOPLE, Lopez said the couple was trying to have a baby last year, and began to accept the idea of being a family of only four if they did not conceive before 2018 was over.
"If it didn’t happen, it wasn’t meant to be. Not part of God’s plan. We have one of each," Lopez told the magazine. "But it got in there! It snuck in, towards the end, so a bit of a Christmas miracle."
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The couple announced news with a couple of cute posts on Instagram. First, Lopez published a video of his family sharing the latest, along with son Dominic "Nico" Luciano, 5, and daughter Dia Francesca, 8, chiming in. Then, Mazza shared a photo of Lopez kissing her baby bump, and with their children wearing "big sister" and "big brother" shirts. Even their French Bulldog, Julio Cesar Chavez, joined in on the fun with a "big brother" shirt.
Lopez, 45, said Nico and Gia were surprised to learn they are getting another sibling when they heard the news.
“At first they were like, ‘Wait, what?’ They couldn’t understand. It took a second for it to register,” the former Saved by the Bell star said. “My daughter got very dramatic. She was like, ‘If I have another brother, I’m telling you right now, I’m moving to Texas!’"
Lopez said the couple plan to keep the baby's gender a surprise until he or she is born.
“We’ve waited for all the kids, [so] it’s going to be a surprise," Lopez explained to PEOPLE. "We’re pretty old school, you know, it being the tie-breaker. It doesn’t matter, to be honest, as long as it’s healthy. We’re just very excited. The gender reveal will be when it’s born!"
They did make one change though. Lopez said they announced Mazza's pregnancy earlier than in the past, because the 36-year-old "didn't want anyone thinking she was gettying fat." But Lopez said Mazza "looks great" when she is pregnant.
Mazza's pregnancy has gone well so far, but their kids are being very protective.
"The kids tend to her. They’re always kissing her belly," Lopez said. "They’re very excited. It’s really neat to see how the kids react."
Lopez and Mazza have been married since 2012, with Gia serving as their flower girl. After the wedding, Mazza said Lopez wanted to have four children.
"Mario is trying to convince me to have four kids," she told Us Weekly at the time. "I said I would have three — that was pushing it."
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