Actress Pam St Clement announced in July that she is leaving the BBC One soap after 25 years in the iconic role.
Pat will reportedly be killed off in "emotional" scenes at Christmas, coinciding with the return of Bianca (Patsy Palmer) and Ricky Butcher (Sid Owen). However, the exact cause of her death is yet to be revealed.
"Pat is one of the soap's biggest-ever characters, and after much deliberation over her exit it was decided she will be killed off," an EastEnders insider told the Daily Star Sunday. "Her exit will be one of the most emotional we've ever done.
"She'll enjoy one last Christmas with her family all around her before she goes. Everyone has been sworn to secrecy over the exact details of her death but it will be sudden and heartbreaking.
"Her family will be left devastated by their loss and we're certain it will pull at the heart strings of even the most hardened of EastEnders fans. It's going to go down in history and will be one that the soap world will never ever forget."
The insider added that Pat would never just leave in the back of a black cab, labelling the forthcoming episodes as a "must-see".
An EastEnders spokesman said: "There has been a lot of speculation about Pat's departure. However we are not going to comment as we do not want to spoil it for the viewers."
St Clement's co-stars Barbara Windsor and Patsy Palmer led tributes to the soap star after she announced her exit, with Palmer describing her as an "amazing actress".