The 33-year-old star - who has two sons Sean Preston, five, and Jayden James, four, with ex-wife Britney Spears - is reportedly expecting his fifth child with girlfriend Victoria Prince.
While this will be Prince's first child, Federline is also dad to Kori, eight, and six-year-old Kaleb, his children with ex-girlfriend Shar Jackson.
Prince is reportedly five months pregnant.
The pair have been dating for more than two years.
A source close to the couple told E! Online: "They are totally happy."
Father of the year
Kevin - who divorced Spears in 2007 after three years of marriage - still officially has sole custody of the former couple's sons Sean and Jayden, although the youngsters currently split their time between both parents.
In 2008 Federline was named Father of the Year by Las Vegas nightclub Prive.
Meanwhile, in November 2007, Details magazine named Kevin as one of their Fathers of the Year, alongside the late Anna Nicole Smith's ex-partner, Larry Birkhead.
At the time, the magazine explained: "The New Dad, as represented by Kevin and Birkhead, is involved. He trucks the kids to the supermarket, decorates their bedrooms, and even lets them dictate the direction of his career."