Nicola Roberts said her 'heart is aching' after the death of her Girls Aloud bandmate Sarah Harding.
Sarah's mum broke the news in a heart-breaking post on Instagram this morning that her 'shining star' had died aged just 39.
She was diagnosed with advanced breast cancer last year.
Nicola said she is 'absolutely devastated' by the news and 'can't accept that this day has come'.
She said it's 'unthinkable' and 'utterly cruel' that Sarah has passed away in a touching Instagram post.
READ MORE: Mum's heart-breaking tribute as Sarah Harding dies, aged 39
In full, the post read: “I’m absolutely devastated and I can’t accept that this day has come.
"My heart is aching and all day everything we went through together has raced round my mind.
"Especially this last year since her diagnosis, as hard as the year has been, our new memories are strong in my heart.
“There are so many things to say and at first it felt to personal to put them here and then I remembered that there are so many other people grieving her too.
"A part of me or us isn’t here anymore and it’s unthinkable and painful and utterly cruel.
"She would have loved your messages today.
“Electric girl, you made us. You gave it everything and still with a smile.
"A white butterfly flew past my window this morning before I knew, it must have been you.”
Nicola also shared a series of pictures of her and Sarah together in the early years of Girls Aloud.
Tributes have been flooding in for the popstar today, with former bandmate Nadine Coyle also posting a touching post on Instagram.
"I am absolutely devastated!!" said Nadine as she sent her love to grieving fans.
"I can’t think of 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."
The girl band were formed on the ITV talent show Popstars: The Rivals back in 2002.
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