LOS ANGELES -- "Dancing with the Stars" celebrated 20 years in the ballroom on Tuesday night, and the show did it in a big way.

Producers invited dozens of favorite past competitors and pro dancers, along with former host Tom Bergeron, who joined in on the judge's panel.

Previous mirror ball champ, and now judge, Derek Hough choreographed an opening routine that included the six original professional dancers from Season 1: Alec Mazo, Ashly DelGrosso, Louis van Amstel, Jonathan Roberts, Charlotte Jorgensen and Edyta Sliwinska. They set the tone for a big reveal of all the current pros finishing an elaborate dance.

As far as the competition, the couples each performed a new style of dance. Robert Irwin and Witney Carson earned the first perfect 40 of the season for their foxtrot. Robert

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