Brett Oppenheim Says Jason Loved Chrishell More Than Anybody Despite Split

Jason Oppenheim and Chrishell Stause are both back on the market, and although some "Selling Sunset" fans doubt the relationship was ever real ... Jason's twin bro says it was real, and really serious.

Brett Oppenheim was leaving his famous real estate agency on Sunset Tuesday when he shot down rumors Jason and Chrishell were only faking a relationship to promote the show's current season. Instead, he says, "My brother and Chrishell love each other more than Jason has probably loved anybody."

As we've told you, the 'Selling' costars announced Tuesday they're calling it quits, 5 months after they started dating ... a relationship Brett has publicly supported from day one. When Chrishell first posted pics from their romantic European getaway, Brett commented ... "Love you Chrishell. Thank you for making my brother happy."

The breakup's still fresh, but he's confident they truly loved each other. As for why they split -- Brett was pretty mum, but Jason himself hinted it might be because only one of them wanted to have kids.

His breakup post on IG said, "While we have different wants regarding a family, we continue to have the utmost respect for one another."

Just last week, Chrishell told us height doesn't matter in a relationship when we asked her thoughts about dating a shorter guy --- after Tom Holland and Zendaya weighed in on the double standard.