Viewers will see Pat – played by Pam St Clement since 1986 – leave the BBC programme over the festive period, although makers of the soap are keeping the date of her death under wraps.
St Clement, 69, joined the soap the year after it launched and announced she was leaving over the summer.
Viewers have known Pat is to die, but the cause of her death has been closely guarded with bosses working on three alternative endings.
EastEnders is up against Downton Abbey in the ratings war on Christmas Day, but as is often the case, the festive season will not be an occasion for cheer in Albert Square.
It has been reported that Pat will say her final farewells after being diagnosed with terminal cancer.
In the coming days Walford fans will see her face nephew Derek Branning (Jamie Foreman) while she lies helpless in bed. And he in turn rows with Pat’s son David (Michael French), returning to the show after he quit the Square in 1996.