Kelly Clarkson full-on broke down -- not once but several times -- during her incredibly emotional return to the "American Idol" stage ... an appearance that brought the judges to tears.
Kelly sang her song, "Piece by Piece" -- a song about her dad abandoning her and how she would never do that to her child. Kelly, who's 9 months pregnant, couldn't handle it and had to stop mid-song.
The first 'A.I.' winner had turned her back on the show that made her famous. For many years she tried to shake the show off her back, but in its final season she's embracing it again.