The actress will be back on screen as Peggy Mitchell in the autumn as part of a new storyline for her on-screen son Phil (Steve McFadden).
When Peggy learns that Phil needs her help, she acts true to form and decides to put family first by returning to Walford.
Speaking of her comeback, Windsor commented: "It is no secret how much I have always loved EastEnders and Peggy Mitchell, and by the number of times I'm constantly stopped by the great British public and asked either 'When are you coming back?' or 'Please say, get out of my pub', it seems they have too.
"It may only be a short visit, but it's a family matter and as Peggy always said, 'It's all about family'."
EastEnders' executive producer Lorraine Newman added: "We're delighted to announce Barbara's return for a very special episode. Peggy's surprise visit is a wonderful treat for our fans, as well as the cast and crew here on EastEnders. It's great to welcome her home."
Show chiefs have promised that Peggy's brief return is part of a "huge autumn" for EastEnders which will see the Mitchell family take centre stage.
With Samantha Womack reprising her role as Ronnie, Roxy planning her wedding to Alfie Moon and Phil set to find himself in trouble once more, the Mitchells have some extremely dramatic storylines on the way.
Windsor bowed out from EastEnders in 2010 after 15 years with the show. Her exit storyline saw Peggy leave Walford after realising that it was the only way Phil would ever sort out his life.
Peggy has since been living in Portugal but has seen Phil while on a brief holiday to Cornwall.
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