Former EastEnders star Nicola Stapleton is to return to the show after 17 years to reprise her role as Mandy Salter.
The actress was last seen as a teenage tearaway, living rough at times and involved with drugs and crime.
Mandy will return to Albert Square in the autumn, the BBC said, giving residents "a shock".
The character left the show in 1994 as she accompanied boyfriend Aidan - played by Sean Maguire - on his return to Ireland.
Since leaving the show after nearly two years, Nicola went on to appear in dramas such as ITV's women's prison series Bad Girls, as well as taking roles in The Bill and Casualty. She also appeared in ITV1's rival soap Emmerdale and a spin-off of Channel 4's Hollyoaks.
Nicola, 36, said: "I'm looking forward to playing Mandy again, it will be interesting to see what she's been up to all this time.
"I'm excited to be coming back and working with some old friends."
Her character is said to have grown up but is still "fun, chaotic and wild, with a spiteful streak".
The BBC said of her return: "Mandy is a manipulative force of nature so it's more than likely she'll be causing trouble for at least one of Walford's well known residents."
Other stars who have returned to Walford after years away include Leslie Grantham as 'Dirty' Den Watts, Jessie Wallace as Kat Moon and Shane Richie as her husband Alfie. Patsy Palmer also made a comeback as Bianca Jackson, while Danniella Westbrook reprised her role as Sam Mitchell.