Kara and Hannah Tointon are set to star together in Mr Selfridge.
The real-life sisters, who have never acted together before, will play screen siblings Rosalie and Violette Selfridge - the daughters of store founder Harry Gordon Selfridge (Jeremy Piven) - in the third series of ITV's period drama.
Kara (left), who won Strictly Come Dancing in 2010 and has starred in EastEnders, will portray Rosalie, with her younger sister cast as her rebellious sibling Violette.
Zoe Wanamaker has also joined the cast as a trouble-making Russian princess, Marie de Bolotoff, with Leon Ockenden as her son Serge.
Sacha Parkinson, who previously played Sian Powers on Coronation Street, will play Kitty Hawkins' ambitious younger sister, while Kelly Adams plays Harry's new love interest, Nancy Webb.
The 10 new episodes of the series, which picks up in 1919 after the end of World War I, will begin filming in London in coming days. The first episode begins with a lavish wedding between Rosalie and Serge.
Kate Lewis, executive producer for ITV Studios, teased that despite the end of the war, Harry will face some difficulties in his life.
"We have some surprises in store for an audience in this third series. You only have to walk down Oxford Street today to know that Selfridges department store continued to be successful, but for its founder, Harry Selfridge, things were very different," she said.
"His story was a roller-coaster ride that ended rather tragically. We pick up series three in 1919, the point at which his life really begins to unravel."
The third series of Mr Selfridge, written by Kate Brooke, Kate O'Riordan and Helen Raynor, is expected to premiere in 2015.
