In the IG Stories, the UFC superstar's longtime partner called Nikita Ni Lamhain -- who just won her civil case against McGregor in Ireland last week -- a liar ... and said straight up, "My sons will be warned women like you exist in the world."

Devlin claimed that back in 2018, prior to Ni Lamhain's suit against McGregor, Ni Lamhain would send "messages and pictures of herself over and over to my man" ... despite knowing he was in a committed relationship.

She also said Ni Lamhain made up her allegations against McGregor -- claiming surveillance footage following Ni Lamhain's now-infamous '18 encounter with McGregor backs up her beliefs.

"CCTV DOES NOT LIE," she wrote. "I look forward [to] the day the world will see the footage of you on that night and the carry on of you."

"Not a bother on you having the time of your life. This is the real evidence, video footage no one knew was being taken in the moment which you miraculously don't remember? To me it looks like you're the one sexually assaulting in the lift. To me it looks like everyone is trying to get away from you."

In a separate post on the social media app, Devlin shared a snap of McGregor and their family ... making it clear she's fully in his corner despite the jury's ruling last Friday.

"I love him I trust him and I BELIEVE HIM!" she wrote. "Our four beautiful children whose smiling faces and happy hearts are testimony to the man he is and who we are!"

"No one is entitled to comment on our relationship -- we trust one another and love one another. Nothing will change that. Our family stands strong!"

For Conor's part, he's been adamant that his intercourse with Ni Lamhain was nothing but consensual ... and he issued a public apology to Devlin for his actions in a statement on his X page on Monday. On Tuesday, he also re-shared one of Devlin's posts, captioning it with a couple emojis.