For the first time since rumors of a surprise pregnancy surfaced last week, Scarlett Johansson showed off what could just be her burgeoning baby bump on the red carpet Thursday.

Promoting her latest film, “Captain America: The Winter Soldier,” the 29-year-old actress and rumored mommy-to-be sported a fitted black and white lace ensemble to the movie’s Hollywood premiere, smiling and showing off what is believed to be a 4-month-along baby bump. While Johansson’s fiancé Romain Dauriac was nowhere to be seen, the engaged actress was spotted wearing the diamond engagement ring given her by her French journalist beau last year.

Earlier in the week, Johansson played coy when asked by the Huffington Post about her pregnancy, which she yet to officially confirm, while discussing her role in the coming “Avengers” sequel.

“Everything for ‘Avenger 2’ -- We’re fully steam ahead. We start shooting in three weeks and I’m stunt training and we’re good to go,” said Johansson. “You know, I think it’s something that is hard to talk about, exactly. You know, trying to skirt around your question exactly and, you know, doing a poor job of it. But, you know, like I said, everything is on exactly on schedule.”

While Johansson isn’t ready to open up about her alleged impending arrival just yet, Jon Favreau, her co-star and director in the coming film “Chef,” was more than happy to discuss the actress’s mothering abilities. “She’ll be wonderful,” Favreau told E! News at the film’s South By Southwest festival premiere in Austin last weekend. “She’s one of my favorite people because she’s smart, she’s talented and she’s really down to earth and a hard worker,” he said.

Last week multiple sources confirmed to Us Weekly that Johansson was expecting her first child with Dauriac. According to the insider, the pregnancy was a shock for the engaged couple. “The baby was a welcome surprise,” said the source. “She’s just excited to share the news.”

Johansson and Dauriac were last spotted together taking in the 2014 Cesar Film Awards in Paris on Feb. 28. During the ceremony, filmmaker Quentin Tarantino presented her with an honorary Cesar.