"Kylie, you're 22 and you've always been one year cooler than me," Richie, 21, says in the clip. "But I love you. You're my best friend. I don't know what life would be like without you."
"Throwback to the most beautiful trip of my life!!! Wish i could turn around time ? thank you @amberasaly for this video," Jenner captioned the post, which also included snippets of her mom, Kris Jenner, boyfriend Travis Scott, daughter Stormi and other friends.
Jenner and Richie met as kids, but have visibly gotten closer in recent months, in the wake of the Kardashian family's falling out with Jenner's former best friend, Jordyn Woods.
Woods, meanwhile, addressed her strained relationship with Jenner in an interview with Teen Vogue last week. When asked about their "breakup," Woods hesitated before asking, "What's the definition of a breakup?"
"'The separation or breaking up of something into several pieces or sections. The end of a relationship,'" she read after looking up the definition on her phone. "Those are the two things. What I’d ask is, 'Does anything really end? Or is it a cycle?'"
"I love her. That’s my homie," she said. "I hope everything falls into place and that we can all grow and build our relationships with our family and God and come back together one day and be stronger and happier."