This new 54-year-old parent is not an ageing roué with a wife young enough to be his daughter, but a woman with a husband young enough to be her son. "Family getting larger", she captioned one post.
Soon after the Danish beauty icon posted a second photo, this time with the caption: "Happy time".
Brigitte, who was once married to Sylvester Stallone, showed off her baby bump in a curve-hugging gray dress while making the announcement.
The publication also said Nielsen had been seen lunching in West Hollywood the last few months and did a good job of concealing the pregnancy. Nielsen is already mom to four sons: Raoul Meyer Jr., 23, Douglas Meyer, 25, Killian Gastineau, 28, and Julian Winding, 34.
Nielsen was married to Sylvester Stallone from 1985-87, but she and the "Rocky" actor didn't have children together.
Congrats to Brigitte and Mattia on the wonderful news!
The "Cobra" actress has been married to Italian Mattia Dessi since 2006, and turns 55 in July.
This will be the Playboy model's fifth child.
At the time, she said she was still on good terms with Jackie and the pair were occasionally in touch. Brigitte wore a pink rose tiara for the beach-side ceremony, with both she and her new husband jumping into the hotel pool immediately after saying "I do".