The actress, 55, tells PEOPLE that she was seven and a half months pregnant at the time the cameras went up on the Steven Caple Jr.-directed film, and hid it from everyone.
“I was so nervous and I was trying to hide it in my ivory suit, which we did,” she says. “It was a very first big day.”
Lucky for Nielsen, the Danish actress and reality star was able to keep it under wraps, even when she came back for another round of filming.
“No one found out,” she says proudly. “The second time around, we shot it over twice and I had to wait three and a half weeks and my tummy did grow in that time but we got away with everything. Everybody was happy.”
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Nielsen gave birth to daughter Frida on June 22 at the age of 54. She shares the baby girl with her Italian model husband Mattia Dessi and is already mom to sons Raoul Meyer Jr., 23, Douglas Meyer, 25, Killian Gastineau, 28, and Julian Winding, 34 — all of whom she calls “four gorgeous, tall bodyguards.”
“They are totally in love with her,” Nielsen says of Frida’s older brothers. “She is their little princess.”
Despite it taking more than 10 years of in vitro fertilization for Nielsen to conceive, she says she had “a very easy pregnancy.”
“This is my fifth pregnancy and all of them have been different,” she says. “My first one was very difficult, two of them were very easy and with Frida, my little baby girl, it was very, very easy. No complaints. I was really lucky.”
Since then, Nielsen’s body has already bounced back — though she doesn’t have any big secrets as to how.
“I am not really sure,” she remarks. “I thought at my age with pregnancy, who knows how your body will fall back together? I said, ‘Whatever happens, happens. I am going to give myself the time to bond with my daughter and give my body a break.’ For some strange reason, already two, three weeks after I gave birth, I lost the weight.”
“Now it is just about getting into the gym and getting fit again,” Nielsen adds. “But I feel really good!”
And until then, Nielsen — who is currently spending the holidays in Europe with her husband and daughter — says this past year has given her many reasons to be grateful.
“2018 has given me the best of everything — a beautiful daughter, we are healthy, we are happy and my career is moving forward. One cannot ask for anything more,” she raves. “We have been shedding a lot of happy tears.”