Zach Galifianakis' Baby Delivered By Kardashians' OB/GYN

Zach Galifianakis' newest baby boy will be forever tied at the belly button to the Kardashians ... since his pops used Kim, Kourtney and Kris' same OB/GYN.

Zach's son, Rufus Emmanuel Lundberg, was delivered by none other than Dr. Paul Crane, who also delivered all the Kardashian babies as of late ... including Dream.

According to the birth certificate -- obtained by TMZ -- Rufus was born on Nov. 7 this year at Cedars-Sinai Medical Center to his parents Zach and Quinn Lundberg.

It's strange ... Zach and Quinn have been married since 2012, but Rufus bears his mother's surname for some reason. Maybe Galifianakis was too much of a mouthful -- heck, maybe Kardashian would be more appropriate.