Cheryl, Nicola Roberts, Nadine Coyle, and Kimberley Walsh remembered the "stunning, unique, crazy, quirky, kind" Harding after her death at 39.

The members of Girls Aloud are singing emotional praises for their late bandmate Sarah Harding, who died Sunday at 39 following a battle with breast cancer.

"Although we knew this day would arrive I am somehow still feeling at a loss for words that our stunning, unique, crazy, quirky, kind and soft hearted girl has departed," Cheryl wrote on Instagram, adding that she's navigating "painfully strange and horribly unfamiliar waves of disbelief and finality" after losing Harding. "I wanted to make sure you knew just how much your love and continued support meant to Sarah through her most vulnerable times. She was so grateful and you really lifted her spirits when she needed you most. I also realize so many will be deeply affected by the circumstances of Sarah's passing… I am sending you all so much love. I love you Sarah… farewell."

Nicola Roberts also shared a photo of herself and Harding, saying she was "devastated" by her friend's death. Still, she celebrated "new memories" that remain "strong in [her] heart" amid the painful year since Harding's cancer diagnosis.

"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," she wrote. "There are so many things to say and at first it felt too 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."

Nadine Coyle admitted she was at a loss for words "that could possibly express" her sadness, and expressed love and appreciation for the girl group's fans. Kimberley Walsh added that she'll miss hearing Harding's "infectious chuckle" most of all.

"Your fire burned so bright and you loved, lived and laughed so hard," Walsh wrote. "Sending love and strength to everyone who is grieving today. My heart is broken."

Harding's mother confirmed her daughter's death in an Instagram post over the weekend, writing that she hoped supporters would remember her for being a "bright shining star" instead of for her "fight against this terrible disease."

Following their formation on the 2002 reality competition series Popstars: The Rivals, Girls Aloud became one of the most successful female groups in English music history. They charted four No. 1 singles on the U.K. charts, with Cheryl also breaking out as a successful solo act (with six No. 1 songs ) after the band's hiatus in 2009. Girls Aloud's last release as a five-strong act came in 2012, when they dropped the greatest-hits album Ten in celebration of a decade in the industry.

Girls Aloud
Girls Aloud members Sarah Harding, Nadine Coyle, Nicola Roberts, Cheryl, and Kimberly Walsh
| Credit: Eamonn McCormack/WireImage

Before Harding's death, she released solo material as well, including the 2015 EP Threads and her final release, "Wear It Like a Crown," which premiered in March. She also wrote a memoir, Hear Me Out, which published earlier this year.

Related content: