Rob Kardashian made a rare appearance at his sister Khloe Kardashian's milestone birthday dinner. The Good American founder turned 40 on Thursday and shared a snippet of her celebration on social media, where Rob made a surprise cameo.

In an Instagram video, Khloe is seen enjoying an intimate dinner with family and friends, including Rob, her best friend Malika Haqq, and her grandmother Mary Jo "MJ" Campbell. Rob appeared to be having a great time, cheering on Khloe as she was presented with a beautifully decorated birthday cake.

This is the second time this month that the usually private Rob has appeared in the public eye with the Kardashian-Jenner family. He recently appeared over the phone on an episode of "The Kardashians," though it was a brief appearance.

In that episode, Rob had an NSFW conversation with Khloe about his penis, as she was trying to acquire sperm for her best friend Malika. These appearances suggest Rob isn't completely avoiding the spotlight as he used to.

Khloe and Rob have always shared a close bond, being the youngest Kardashian siblings. Rob's recent actions seem to indicate his willingness to support his sister in any way.

As for Khloe, she's embracing turning 40 and looking forward to this new decade, leaving behind the drama of her 30s.