Sources connected to the former duo tell us they ended things shortly after a lengthy trip to Japan ... unclear who broke up with who. The split news also comes on the heels of photos that popped up this weekend of Kanye at a movie with another woman.

Kanye and Chaney first started hanging out back in February -- just as things were cooling off between Ye and Julia Fox. The model and Kim K look-alike started popping up at 'Donda 2' events Ye was hosting.

It wasn't long before they started showing up in the same photographs together, and eventually -- they stopped hiding their relationship ... going public as boyfriend and girlfriend.

While their romance ended up being short-lived, they sure did a lot in each other's company ... jet-setting all over the country for different events -- mostly between Miami and L.A., though -- and even took the international trip to Japan.

Not much was known about Chaney for a long time other than the fact that she was a dead ringer for Kanye's ex -- and eventually, amid all the speculation, she introduced herself to social media -- highlighting differences between her and Kim.

She said she was a COO of a mental health org, and not just that -- but added she was in school getting her Master's. Chaney also noted she'd never had any surgery done on her face.

Things seemed to really be getting serious between the two -- Chaney got a "ye" tattoo on her wrist. So from the outside looking in -- they were all about each other.

Of course, she's also much younger than Kanye -- he's 44, and she's in her mid-20s. It's a similar age difference to what Kim and Pete Davidson share, but they're going strong.