Bruce is gone and he's not coming back -- 'cause Caitlyn Jenner is NOT transitioning back into a man ... despite reports to the contrary.
The rumors stem from famous biographer Ian Halperin -- who claimed that while researching Caitlyn for a book, was told by a source that she was experiencing "sex change regret" and was considering de-transitioning back to a man.
Halperin says multiple sources close to the Kardashian family said the move wouldn't surprise them.
But Caitlyn's rep is calling full BS on the report -- telling the NY Daily News, "Of course it's not true.