"Words cannot express the joy my children bring me," wrote Britney Spears' ex husband alongside a photo of an 'It's A Girl' floral arrangement.
"Words cannot express the joy my children bring me"
"We are very excited to welcome the newest member of our family. I love you with all my heart @crownv_16," Kevin added, tagging Victoria.
It's the second child for the couple, who were married in August 2013, but the sixth for the former backup dancer.
He and Victoria have a two-year-old daughter named Jordan; he has two sons, Sean, eight, and Jayden, seven, with Britney, as well as two children with ex-girlfriend Shar Jackson, Kori, 11, and Kaleb, nine.
So far, no further details about the new arrival have been revealed.
Britney with her and Kevin's sons Sean-Preston and Jayden Federline
Kevin surprised Victoria with a proposal during a "work trip" to Las Vegas last year. Getting down on one knee, he said, "Victoria Prince, will you marry me in two days, infront of 30 of our closest family and friends?"
Kevin with wife Victoria and their two-year-old daughter Jordan
The couple, who had been dating since 2008, tied the knot in an intimate ceremony in the penthouse of the Hard Rock Hotel.