Ritchie also has two sons -- one biological and one adopted -- and a step-daughter with his ex-wife, pop star Madonna, whom he divorced three years ago. Madonna adopted a girl after her divorce from Ritchie, as well.
The Mirror said Ritchie's youngest child was born via emergency Caesarian section at London's Portland hospital Monday morning.
"The baby came a few days earlier than planned, but the actual birth went well and both mum and tot are doing great," an unnamed source close to the couple told the newspaper. "Madonna sent her congratulations. Rocco, Lourdes, and adopted youngsters, David and Mercy, are all being introduced to the new arrival within the next couple of weeks. Both Guy and Madonna are determined to be grown-up about it and remain on friendly terms."