Chrishell Stause was completely blindsided when G Flip decided to end their four-year romance … and TMZ has learned the Australian musician told the “Selling Sunset” alum they now viewed her as more of a friend than a romantic partner.

Sources close to the former couple tell TMZ … their relationship was harmonious, but G’s romantic feelings for Chrishell had faded.

We’re told G recently traveled to Los Angeles from Australia, where the two had a difficult conversation about G no longer being in love with Chrishell in a romantic way.

Our sources say Chrishell is heartbroken over the split.

We’re told the breakup had nothing to do with Chrishell allegedly being “mean” or difficult to get along with … despite claims made by sources close to her former “Selling Sunset” castmates.

Instead, our sources say both Chrishell and G view their time together as a great relationship … but G’s feelings simply changed.

As we reported … Chrishell tearfully announced their breakup Monday on Instagram, admitting she’s still in love with G and feels “a little bit like a failure.” G later said they would always love Chrishell and cherish their memories together.

TMZ previously reported G was the one who ended the relationship, though Chrishell announced the split first.