In a sneak peek at Sunday's episode of I Am Cait, Disick, 32, is hanging out with Caitlyn, 66, at her house in Malibu, California. After helping her fix her broken smoke detector, Disick launches into what a positive change he's seen in Caitlyn since she transitioned last year.
"I see a dramatic change – and not visually so much, but really just emotionally," he tells the camera.
"I mean, I really believe when Caitlyn was Bruce, he was really shut off and angry and just wasn't happy," Disick continues. "And now that she can be who she really wants to be, it's a whole different person and I feel a real connection."
RELATED VIDEO: The Caitlyn Jenner Story: From Olympic Icon to Transgender Hero
Disick, meanwhile, isn't the only member of Caitlyn's family to guest-star on her docu-series this week – ex-wife Kris Jenner will also be featured on the episode.
In a previously released scene, things get intense between the exes when Caitlyn reveals she's transitioning all of Bruce's legal documentation.
In the clip, Kris, 60, is stunned into silence while listening to Caitlyn talk about her new driver's license and updated birth certificate.
"Does this mean he didn't exist?" Kris asks in shock. "Was I ever married? Was I legally married?"
I Am Cait airs Sundays (9 p.m. ET) on E!