Carey Mulligan is reportedly pregnant with her first child

When nominee Carey Mulligan stepped out at the 2015 Tony Awards, it seemed her burgundy Balenciaga gown was hiding a little secret - and according to Us Weekly, that secret was, in fact, her first child with Marcus Mumford. The strapless, floor-length number swooped high at the neck and cut away from the body - in line with the Far From the Madding Crowd star's pared-down aesthetic but far boxier than usual.

Carey wore an oxblood Balenciaga gown at the 2015 Tony Awards, where she was nominated. Photo: © Getty Images

"They weren't planning on announcing, but she hasn't stopped working," says the magazine's source. "Everybody around her is being very supportive."

The actress is just finishing up a Broadway run in the stage play Skylight, opposite Bill Nighy and for which she received a Tony nomination. Once the production wraps, it looks like Carey and Marcus will return to England.

Carey Mulligan and Marcus Mumford at the 2012 Met Gala. Photo: © Getty Images

Though the Great Gatsby star and her Mumford & Sons frontman are yet to confirm the news, they're sure to be fantastic parents to their new addition. The couple have known each other for decades, having first met as childhood pen pals and rekindling their friendship - and romance - years later after they'd both become celebrities.

"They both come from very solid families and have a real sense of the life they want to live," Sienna said of the couple in a Vogue profile of Carey. "Their normalcy. They have chicken and a dog, and roasts and friends, jams by campfires. It's sort of idyllic. Marcus can headline Glastonbury and Carey can be nominated for however many Oscars, and then they come back to their farm, and they're in big woolly jumpers and funny hats, raising piglets."

Adorable Carey and Marcus stole the show at a MusiCares event in 2013. Photo: © Getty Images

Carey and Marcus married in 2012, though the two are generally tight-lipped about their relationship. "Marcus is the only thing that's mine that I can keep away, so I try to," the Oscar nominee told Vogue.

Mumford & Sons are spending the summer touring through North America and Europe.

HELLO! Canada magazine is available for your tablet and smartphone. Get HELLO! Canada, PEOPLE, Vanity Fair and over 100 more of the world’s best magazines for one low monthly price at Texture by Next Issue. CLICK HERE to sign up for a free trial.