Actress Paula Lane - who left drama school only two years ago - joins the Weatherfield soap as Kylie Turner, Becky's half-sister by another father.
Kylie's arrival sends shockwaves through The Rovers as she moves in with her big sister, causing trouble for the rest of the McDonalds in the process.
Corrie producer Phil Collinson exclusively told DS: "Paula's brilliant and I'm very excited. She'll arrive and move into the pub with Becky, Liz and Steve. She's a big character across the next six months and beyond and it's fair to say that she'll cause hell for the McDonalds."
Speaking of her casting, Lane said: "I'm very excited to be joining Coronation Street and to be working alongside Katherine Kelly."
A show source revealed: "Despite only sharing their mother's blood, Kylie's every bit as full-on as Becky ever knew how to be. Kylie has all the characteristics of the Becky we've seen glimpses of over the years - it's like holding up an age-defying mirror."
They added: "It doesn't take her long to set her sights on Irish barman Ciaran, either. She's a little firecracker, definitely one to watch!"
Lane began filming at the soap's home in Manchester last week and will make her screen debut in August.
Our full interview with Phil Collinson will be available later today (Tuesday).