The Take That star tweeted last night: "My wife and I are expecting our 4th child #Anotherowngoal"
He added: "What a lovely bunch you are. Thank you for all your kind messages. We are a very excited family."
Gary then threw down the gauntlet to Peter Andre, saying: "Next goal 'Celebrity Dad of the Year' #moveasideandre"
Gary Barlow tweeted his exciting news last night
Dawn, 42, has had her three-month scan and Gary is "beaming constantly."
The 41-year-old X Factor judge told the Sun: "It's brilliant, we couldn't be happier with the news. We're all just really excited about the new arrival."
Gary and Dawn, who married in 2000 after meeting when Dawn danced on Take That's Nobody Else tour in 1995, have three children: Daniel, 11, Emily, nine, and Daisy, three.
A source said: "Gary is constantly beaming from ear to ear. The news couldn't have come at a better time because he's a real family man and now he can be around more.
"Last year was such a whirlwind with the Take That tour and then the X Factor. Now he can kick back and fully appreciate all that's going on."
Gary's going to skip tomorrow's BRITs, saying: "I'm going to be watching it on the sofa with the Missus. I'm keeping my fingers crossed that Coldplay do the double and Adele gets a fair few."
Congrats to Gary and Dawn!