The notoriously private couple have yet to publicly confirm the news, though they were spotted shopping with both their newborn baby and firstborn, a daughter who turns 2 in November, in Hampstead, England, on Monday, August 14.
The Pearl Harbor actor's rep had no comment when Us Weekly reached out.
Egerton, 28, did not formally announce her second pregnancy, but she debuted her baby bump in a formfitting black gown at an Oscars afterparty in February. She and Hartnett, 39, also sparked engagement rumors at the event, where she sported a stunning diamond ring on her left hand.
Shortly after welcoming their daughter, whose name has yet to be revealed, in November 2015, the Black Hawk Down actor gushed over fatherhood. "It changes everything, what can you say?" he said on Good Morning Britain in May 2016. "The rubber finally meets the road and everything you have done beforehand is just preamble. You're actually living your life for the first time because everything matters a bit more, doesn't it?"
The couple's firstborn changed Hartnett's perspective, too. "Your ego melts away when you have a new kid," the Penny Dreadful star said on Live With Kelly and Michael in April 2016. "Your heart kind of leaves your body and you give it permission to walk around with someone else for a while. It's really terrifying but it's beautiful. I love it more than anything. I wish I would have started it earlier. But I'm so glad that she is the one I'm raising."
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