The Sonia Fowler actress revealed that she is expecting her second child on Twitter on Friday (12 February).
She tweeted: "Evening all... Time to let everybody know that @cameramarc and I are having a baby in the summer. The three musketeers become four."
Evening all... Time to let everybody know that @cameramarc and I are having a baby in the summer. The three musketeers become four.— Natalie Cassidy (@Nat_Cassidy) February 12, 2016
It will be her first child with fiancé Marc Humphreys, who works as a freelance cameraman on the BBC soap.
She has a daughter, five-year-old Eliza, from her relationship with ex Adam Cottrell.
Natalie and Marc announced their engagement last October, after she split from Adam for the second time.
In May 2011, Adam was charged with two offences of assault and two charges of criminal damage after a row between the pair turned physical.
He was sentenced to 120 hours’ community service and Natalie was given a restraining order.
She later got back with him, and they got engaged in May 2013, before splitting six months later.
Speaking about the breakdown of their relationship at the time, she said: "It was my decision. I'm really glad I gave it another chance.
"When kids are involved you almost have to. I can always say to Eliza, 'Mummy tried, but it didn't work out.'"
‘EastEnders’ bosses are said to be currently coming up with ideas of how to temporarily write Sonia out of the soap when Natalie goes on maternity leave later this year.