The cast and crew of Creed II had no idea Brigitte Nielsen was heavily pregnant when she filmed her cameo because she managed to hide her bump with creative clothing.

The Danish actress was invited to reprise her Rocky IV role as Ludmilla Vobet Drago, opposite her ex-husband Sylvester Stallone, for the latest instalment in the boxing film franchise, but she was anxious about missing out on the guest appearance due to her pregnancy.

She didn't tell director Steven Caple, Jr. about her condition, and despite being seven-and-a-half months pregnant at the time of the spring (18) shoot, her baby bump was relatively small, so Brigitte was successful in keeping the news quiet.

"I was so nervous and I was trying to hide it in my ivory suit, which we did," she tells "It was a very big first day (sic). No one found out."

The 55 year old's stylist had another challenge to overcome weeks later as Brigitte was called back for more shoots, but again, their big secret remained under wraps.

"The second time around, we shot it (her cameo) 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," the star shares. "Everybody was happy."

Brigitte welcomed daughter Frida with husband Mattia Dessi in late June (18), after more than a decade of trying in vitro fertilisation (IVF) treatments, and luckily, the Red Sonja actress, who has four adult sons from previous relationships, 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."

Her body has already snapped back post-pregnancy, but Brigitte has no idea how she was able to regain her slender waistline so quickly.

"I thought at my age with pregnancy, who knows how your body will fall back together?" she admits. "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," she adds. "But I feel really good!"