The duo, whose characters are the brother and mother of Jane Beale, will be back for a brief period this summer.
Bosses are yet to reveal what brings them back to the Square, but they are promising that the “shocking” storyline will alter the Beale family forever.
John, who was last seen on Walford during live week, has shared his excitement, stating: “I am thrilled to be able to return to ‘EastEnders’ whilst touring the UK with’ Chicago’.
“Christian is never far from my mind - I turn my back for five minutes and look what happens!"
Jane’s mum, Linda, hasn’t been seen since she left Walford behind in 2009, to move to Florida with her husband Roger.
Catch up on all the latest soap news and spoilers here.
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