Jeff Probst Explains Live Spoiler On 'Survivor 50' Finale

Jeff Probst says he knew he screwed something up on the live taping of the "Survivor 50" finale when the energy in the room suddenly changed ... and he's explaining how the major blunder unfolded.

The longtime "Survivor" host joined us on "TMZ Live" Thursday and broke down the mistake he made live on air, when he announced the loser of a challenge before viewers saw the results.

Jeff says he was backstage preparing for live interviews with contestants as pretaped segments aired ... he wasn't watching the live finale, and was just a little ahead in the script when he came out to talk to Rizo Velovic.

When he told Rizo to go sit down as the rest of the jury, Jeff says he felt the energy shift among the live audience and the contestants on stage ... plus, Rizo was resisting as he pushed him toward a stool.

Jeff says he quickly became aware something was up ... he just didn't know what ... and tells us he didn't even remember what he said until we showed him the clip.

The good news ... Jeff says he learned some valuable lessons about live TV and told us why he has full support from CBS honchos.

Bad news for Jeff ... it sounds like he might finally be forced to wear an earpiece during these things.