Caitlyn Jenner NOT Transitioning Back to a Man ... Rumors Are BS

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."

The rep also called the story "idiotic."