Warner, 36, hinted that the couple welcomed a third daughter in an Instagram post on March 31 by sharing three pairs of shoes for children.
"So proud of these three glorious girls, it's an honour being their mummy..feeling incredibly lucky today," she wrote. Since March 31 was Mother's Day in the U.K., Warner added the hashtag "Happy Mother's Day."
Dornan's rep also confirmed the coupler welcomed their baby to Just Jared, but did not provide further details.
Warner and Dornan, 36, are also parents to daughters Dulcie, 5, and Elva, 3. The couple have been married since 2013.
During an appearance on Live! With Kelly in 2016, Dornan called being the father of two little girls "pretty insane."
"We've got two little girls now, so it's pretty insane. One of my best friends said that one is a pet, two is a zoo," he joked. "It's been a big adjustment and it's definitely harder and you get less time to yourself, but human beings are very good at adaptation. You have to just go with it and accept less sleep and accept less time in your hands and accept less reading of books and washing and all the usual things you do in a day."
At the time, Dornan said he was hoping they would have a boy.
"I think as a guy you just think, 'I'll have a little mini version of myself' or something in a sort of narcissistical (sic) way, but then once you've had girls I can't imagine having [another one]," he told Kelly Ripa.
Dornan is best known for playing Christian Grey in the 50 Shades of Grey trilogy from 2015 to 2018. His other film credits include Anthropoid, The Siege of Jadotville, A Private War and Robin Hood. He played the killer Paul Spector on the U.K. series The Fall, opposite Gillian Anderson, and played The Huntsman in ABC's Once Upon A Time.
As for Warner, she is a former actress who now focuses on her music career. She performed under the name Slow Moving Millie, and also scored the 2017 film Mary Shelley starring Elle Fanning as the writer of Frankenstein.
"It's hard to navigate my career around it and I don't want to exploit the situation, but I'm trying to find my way," she recently told The Independent of her music career while her husband starred in the 50 Shades films. "My way so far has been to be silent as I haven't done any press for anything since Fifty Shades of Grey happened, but I now have pressure to promote my work."
Photo credit: Yui Mok/PA Images via Getty Images