But Carey Mulligan had a very simple way of telling the world she had given birth: she just turned up to work no longer pregnant.

The English actress walked the red carpet twice at the London Film Festival on Wednesday, to promote her new film Suffragette.

It is being reported that Mulligan, 30, gave birth in September, missing the film's premiere at the Telluride Film Festival on September 4, because it was close to her due date.

"Carey has given birth to a healthy and happy baby," a source told E! News.

"She is just enjoying this time with her family and close friends."

Mulligan has been married to Mumford & Sons lead singer Marcus Mumford since 2012.

The pair met as children in London when they became pen pals. They reconnected as adults and became engaged after five months of dating.

It's little surprise that the little Mulligan-Mumford has come without any sort of confirmation from the couple.

The couple never publicly confirmed that Mulligan was pregnant, with Mulligan instead just continuing to walk red carpets with a growing baby bump.

Speaking to Vogue in May, Mulligan explained why she keeps her private life private.

"Marcus is the only thing that's mine that I can keep totally away," she said. "So I try to."

One person who will be happy about the new baby is Factory Girl actress and friend of the couple Sienna Miller.

In the same Vogue profile, Miller described the couple's rural lifestyle as "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," she said.

"It's an amazing balance they've managed to strike. I can't wait for a little baby to come along."