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The announcement was made Wednesday on “Good Morning America.”
Sweetin said her "Fuller House" co-star, Candace Cameron Bure, gave her advice about joining the cast. Bure finished in third place in Season 18 of the hit dancing competition show.
"She’s been really great and excited for me and has shared with me that this is going to be one of the most exciting, overwhelming, physically and mentally demanding things that I’ll ever do, but that it’s incredibly worth it," Sweetin said.
The actress said she brings some dance experience to "DWTS." In one scene of "Fuller House," Sweetin's character dances with "DWTS" pro Val Chmerkovskiy.
"I’ve always loved to dance and Stephanie was a dancer on the show growing up," Sweetin said. "I definitely don’t call myself a professional but I have some experience."
"I have some rhythm so I think I’ll be okay," she added.
Sweetin is the first cast member announced in the line-up for season 22 of the hit reality TV dance competition that pairs stars with professional dance partners.
Sweetin said her professional partner this season is Keo Motsepe.
It’s so fun," Sweetin said of the pair's first few days of rehearsals. "We got through some basic moves of several different styles of dance and just had a lot of fun with it."
"He and I get along really well," she said, calling Motsepe a "phenomenal dancer."
Sweetin is newly engaged and has two daughters, ages and 5 and 8. The actress called her fiance "incredibly supportive" but said she had to keep her "DWTS" role vague around her daughters so they would not share the surprise.
"I mentioned it very briefly to them because they’re eight and five so they’re sort of untrustworthy with secrets," Sweetin said. "Now I can go home and be like, ‘Yeah, yeah, yeah, here’s pictures and here’s all the stuff.’"
"They’ll come to rehearsals and tapings and be very excited," she said. "I think they’ll mostly just like the costumes really."
"Dancing with the Stars" Season 22 premieres March 21 on ABC.