Gillian has decided it is time to focus on other acting roles but has apparently asked bosses that Jean is not killed off, leaving the door open for her to return.
Her character, who suffers from bipolar disorder, has certainly faced some good and bad times since arriving in Walford in 2005.
Jean's medical condition put a huge strain on her relationship with daughter Stacey and son Sean, but there have also been some lighter moments too.
In a statement, Gillian said: "It has been a huge privilege to play Jean Slater these last eight years.
"I treasure the viewers' care and love for the character not only through her hard times but through all the laughter too.
"I will miss EastEnders enormously, but it is time for me to step back and enjoy other acting challenges."
Gillian has won several awards for her portrayal of Jean, including the Best Actress title at last year's Inside Soap Awards.
Jean will make her last appearance on our screens in October.
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