Laura Prepon plays Alex Vause in the TV series 'Orange is the New Black'. Picture: Laura Prepon/Instagram

Laura Prepon made her first appearance on the set of 'Orange is the New Black' on Monday after giving birth to her first child in August.

The 37-year-old actress and her fiancé Ben Foster welcomed a baby daughter - whose name they are yet to unveil publicly - into the world last month, and on Monday Laura shared a picture of herself back on the set of the new series of Netflix blockbuster 'Orange is the new Black' as alter-ego Alex Vause.

She captioned the post: "Back at work! @oitnb season 6! #workingmom #herewego #alexvause (sic)"

Back at work! @oitnb season 6! #workingmom #herewego #alexvause

A post shared by Laura Prepon (@lauraprepon) on

The dark-haired beauty previously said she intends to keep her baby out of the spotlight, hence not revealing her moniker.

She said: "I'm creating life and it's so incredible. I'm so ecstatic for this experience, but you go through so many changes. We've been in the Pacific North West keeping it low-key. I'm a very private person."

Laura and the 'Hell or High Water' star, 36, have been publicly dating since July 2016, but have been friends for more than 20 years.

The pair were engaged by October last year and Laura debuted her baby bump at the Sundance Film Festival in Utah in January this year.

The author - who previously dated Christopher Masterson, the brother of her 'That 70s Show' co-star Danny Masterson, for seven years - previously discussed her amazement at how quickly things have progressed with her relationship.

She said: "It's kind of weird, 'cause it sneaks up on you where you're like, 'I can't believe it's been eight months already. But then you're like, 'Oh my God, she needs to like come out already.

"It's so wonderful. It's such a blessing. She likes it here - she's already kicking!"