Ms Harding died this morning after a tireless but brave battle against the ravages of cancer.
She was just 39.
In a post on her Instagram account, Derry’s Nadine wrote: “I am absolutely devastated!!
“I can’t think of the words that could possibly express how I feel about this girl and what she means to me!!
“I know so many of you will be feeling this way.
“For now I’m sending so much love to you.”
Her post ended with two heart symbols.
News of Ms Harding’s heart-breaking death was announced this afternoon by her devastated family.
In a post next to a black and white image of Harding, her mother wrote: “It’s with deep heartbreak that today I’m sharing the news that my beautiful daughter Sarah has sadly passed away.
“Many of you will know of Sarah’s battle with cancer and that she fought so strongly from her diagnosis until her last day. She slipped away peacefully this morning.
“I’d like to thank everyone for their kind support over the past year.
“It meant the world to Sarah and it gave her great strength and comfort to know she was loved.
“I know she won’t want to be remembered for her fight against this terrible disease – she was a bright, shining star and I hope that’s how she can be remembered instead.”
Earlier this year, in an extract from her memoir Hear Me Out published in the Times, Harding wrote: “In December my doctor told me that the upcoming Christmas would probably be my last.”
She said she didn’t want an exact prognosis, just “comfort” and to be “pain-free”.
Harding shot to fame in 2002 as a contestant on Popstars: The Rivals – an ITV talent show which aimed to find both a new girl band and boy band.
She made it to the final and gained the final spot in the group which became Girls Aloud – despite being the underdog according to bookmakers – alongside Nicola Roberts, Nadine Coyle, Kimberley Walsh and Cheryl Cole (then Tweedy).Tags: