Actress Sienna Miller has revealed her third baby was a boy, while discussing how “complicated and hard” it was to promote her latest film while almost five weeks post-partum.

The 44-year-old actress is best known for roles in Alfie, American Sniper and Factory Girl – and stars opposite John Krasinski in her latest project Tom Clancy’s Jack Ryan: Ghost War.

The couple have a son and a daughter, whose names have not been shared publicly, and Miller also has teenage daughter Marlowe from a previous relationship with actor Tom Sturridge.

In an interview with British Vogue, the actress discussed becoming a mother again in her 40s, and the difficulties of navigating motherhood alongside her busy work schedule.

Reflecting on becoming a mother-of-three, Miller said: “I had thought, by the time I was 40, that it wouldn’t happen.

“That I’d have my one baby and I kind of made peace with it.

“It was such a surprise, and it was such a bonus that I was just euphoric. I felt existentially relieved.”

Miller recounted feeling “quite abandoned” after the birth of her first daughter, and told the fashion magazine: “There wasn’t as much focus on post-partum then.

“I remember people saying to me, ‘I’m not going to ring you because you’ll be in your blissful little bubble’, and feeling so disappointed that it didn’t feel like that.

“I felt like I’d really failed.”

However, the star said the period after welcoming her second child was “just bliss” as she had “wanted another baby for so long”.

“I also had the world’s easiest baby – she barely cried! She was so content. She was so peaceful,” Miller said.

“Of course, the hormonal shift happened, but I felt very cocooned.”

The Bafta-nominated actress recounted boarding a flight to New York City to film an episode of The Tonight Show Starring Jimmy Fallon whilst four-and-a-half weeks post-partum.

“It was all too much. I thought I could manage it, but it was just complicated and hard,” she said.

She told the magazine she cut her schedule in half, but found admitting you “actually just can’t cope” was difficult.

“The power of ‘no’ in motherhood is very important to learn,” she added.

Miller rose to fame in films such as Layer Cake alongside Daniel Craig, and also starred in Alfie opposite Jude Law, who she went on to have a high-profile romance with.