Courtesy knoxedoutnumbered/Instagram

Genevieve “Genna” Knox knows better than most that life is full of surprises.

In 2019, she and husband Kyle were looking to add to their family and give their son, now 6-year-old Liam, a younger sibling. At 38, Genna was relieved to have gotten pregnant easily and things were going smoothly until her 20-week ultrasound came with a huge surprise.

Sharing her story with Today, Knox explains that the ultrasound technician asked whether they were having twins.

“No, I’m not,” she told the tech. “Then I looked up and I could see clear as day that there were two babies.”

The California fifth grade teacher says that she and her husband felt like the “luckiest people in the world” when they learned they would welcome multiples.

Never miss a story — sign up for PEOPLE’s free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

Mom with ‘Secret Triplets’ Reveals How She Found Out She Was Expecting More Than One Baby
Courtesy knoxedoutnumbered/Instagram

“I started having kids later in life, and I didn’t know if I’d even be able to have one,” she says. “We were overjoyed.”

The couple would have nine weeks to get used to the news before another bombshell came their way. During a 4D ultrasound, the sonographer asked Knox when she found out she’d be having twins.

“I said, ‘Oh, gosh you’re not going to believe it,’ and then I told him what happened at the 20-week scan,” only to learn from the tech that she would be welcoming triplets.

“I barely remember anything else about the moment,” she recalls. “I was in total shock.”

Knox made it through 33 weeks of pregnancy before her triplet baby girls — Kaylee, Lily and Cecilia — were born.

Today, Knox documents the family’s adventures across social media, and says that her “hidden triplet,” daughter Cecilia, stands out among the crowd.

“She has a very big personality,” Knox shares. “She is hilarious and we love her to death, but she definitely marches to the beat of her own drum.”