Singer Bernie Nolan was first diagnosed with breast cancer in April 2010.
She received the all-clear in 2012 after a mastectomy and extensive chemotherapy.
But later that year her cancer returned, having spread to her bones, brain, liver and lungs.
Her husband Steve finished her memoir Now and Forever in early 2013 when she became too ill to finish the book.
She died peacefully on Thursday morning surrounded by family members, a spokesman said.
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The Friends star had reportedly not seen her mother for several years following a feud - but reconnected with her shortly before she died.
A deal is believed to have been reached with official confirmation likely on Friday.
The woman is described as being around 50 years old with short spikey purple hair.