Kourtney Kardashian has said ex-boyfriend Scott Disick's substance abuse issues were a "deal-breaker" for their relationship.
The reality star made the claim in a teaser for a reunion show that will air after the final episode of.
The series, which became a pop-culture juggernaut and brought global fame for the family, will come to an end this week after 14 years and 20 seasons.
The Kardashian-Jenners sat down with US TV host Andy Cohen for what has been billed as a nothing-off-limits discussion about their lives.
In the trailer, Kourtney, 42, is asked about her relationship with Disick — the father of her three children — and if it would have survived if it had not been so exposed to the public eye.
"I think the substance abuse was a deal-breaker," Kourtney says, before Disick, 38, admits: "I was pretty irresponsible."
Cohen then asks Disick about his feelings on Kourtney's relationship with Blink-182 drummer Travis Barker.
"So do Kourtney and Travis have your blessing?" Cohen says.
Kim Kardashian West, the star of the family's TV show who built a global brand from its success, also features in the reunion trailer.
She discusses a mystery moment between her and her mother Kris Jenner.
Jenner, 65, adds: "And I'll take care of it."
Kardashian West later says she "absolutely" owes an unnamed man an apology.
The two-part reunion, due to air in the US later this month, will also explore the cheating scandal between Khloe Kardashian and basketball star Tristan Thompson, as well as Jenner's relationship with former partner Caitlyn Jenner.