Other contestants include:
• "General Hospital" star Kelly Monaco.
• Former 98 Degrees boy-band member Drew Lachey.
• Super Bowl champ Emmitt Smith.
• Indianapolis 500 winner Helio Castroneves.
• Olympic medalist speed skater Apolo Anton Ohno.
• "The Bachelor" star Melissa Rycroft.
• Actor Gilles Marini.
In a break from the past, viewers can vote online for the 13th contestant from three former contestants including actors Kyle Massey and Sabrina Bryan and celebrity stylist Carson Kressley. Deadline for filling this 13th slot is Aug. 24, with the winning candidate announced on "Good Morning America" three days later.
"This is about giving the viewers a treat, and breaking the rhythm of the show," said executive producer Conrad Green during a panel at the Television Critics Association conference.
Host Tom Bergeron said he was looking forward to being reunited with past contestants who became friends.
"There's going to be an element of camaraderie that I think will be evident right out of the gate," he said, which will allow him to relate to them not unlike the way he connects with the show's judges "with banter and occasional snarkiness," he laughed.
Among the celebrities gathered for the panel, Bristol Palin in particular was in the crosshairs of reporters, including one who asked her how she would feel being partnered with a gay dancer. (Just fine, thanks.)
Asked why she was subjecting herself, once again, to the scrutiny of the media as a "Dancing" contestants, Palin replied, "I just think that God provides opportunities like this, and you can either go out and do them or not do them, and I figure the press will be talking about me, no matter what."
But as the daughter of former vice presidential candidate Sarah Palin and, like both her parents, a reality star, has she made herself "more vulnerable by making reality television the Palin family business?" another reporter asked.
"I definitely don't think it's our business," said Palin. "You guys will be talking about us either way, and I might as well be doing something enjoyable and fun and with a good group of people."
"You haven't really gone full Kardashian," Bergeron cracked.
"Dancing" returns for its 15th season on ABC on Sept. 24.