The Take That star, 48, shared the exciting news on Twitter, just 10 months after welcoming his third son, Bowie.
“Guess what?” he wrote on Monday 10 October.
“Me and Katie are happy to announce we will have our second child in Feb. Yay! No more sleep for another two years!”
Donald is already dad to 17-year-old Grace and 11-year-old Lola from his previous relationship.
People were quick to point out on Twitter that the couple didn’t wait long after Bowie to have another baby.
He tweeted at the time: “Bowie Taylan Donald came into this world on Tues 12th Jan. Mummy and daddy suffering sleep deprivation but life is wonderful, he is divine.”
Donald and Halil starting dating in 2011 and married in January 2015.