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The newest addition will be a little brother or sister for the couple's two-year-old son.
He or she was conceived with IVF after Natasha suffered an ectopic pregnancy in 2010.
She had to have emergency surgery and Chris later revealed she almost died.
Chris revealed Natasha was expecting in November in his Mail on Sunday column.
He wrote: ”Mrs E is in the family way once again. And yes, I can confirm she is... Thank you so much to the people who made it possible.
"We are eternally grateful. You make dreams come true.
"My wife and I couldn’t be more thrilled . . . Like a lot of couples, becoming pregnant this time was not easy and to the extent that it was beginning to feel like it may never happen."
Chris also has a 25-year-old daughter, Jade, from a previous relationship.
His former wife Billie Piper welcomed her second son, Eugene Pip with actor Laurence Fox last month.
Chris Evans introduces his 'little belter' baby Noah to the world
Billie and Laurence show off their little Pip
It's a little princess!