The momentous event happened at an 18th birthday bash thrown for their daughter, Kylie, where Kris and Caitlyn arrived together.
The photo shows Caitlyn and Kris posing with Kris' daughter Kim Kardashian, who posted the shot on Instagram (along with several other shots from the party) with the caption "The parent trap."
Kris and Caitlyn Jenner were married from 1991 until Kris filed for divorce in September 2014. Their split was finalized last December, before Caitlyn publicly came out as transgender.
Check out their selfie here: