The couple already have two children together -- three-year-old Henry Gunther Ademola Dashtu Samuel and two-year-old Johan Riley Fyoder Taiwo Samuel. In addition, Seal is also the adoptive father of five-year-old Helene "Leni" Klum, Heidi's daughter from a previous relationship with Italian businessman Flavio Briatore.
The Project Runway host had previously expressed that she was hoping for her fourth child to be another girl.
"We'd be happy with either," she told Us. "But it would be a lie if I said we all weren't hoping for a little girl -- especially Leni, because she would love to have a little sister."
Seal and Klum -- who were married in May 2005 -- recently celebrated their fourth wedding anniversary.