'Confessions of a Shopaholic' Author Sophie Kinsella Dead at 55

Sophie Kinsella -- the powerhouse author behind the hit 'Shopaholic' book series -- has died at 55, three years after being diagnosed with brain cancer.

The British writer’s family broke the heartbreaking news on her IG Wednesday ... saying even though she battled her illness with unbelievable courage, she ultimately passed away peacefully ... spending her final days wrapped in "family and music and warmth and Christmas and joy."

Sophie first shared her cancer diagnosis just last April ... revealing she had glioblastoma -- the most aggressive form of brain cancer -- but told fans she’d undergone a successful surgery and was pushing through radiotherapy and chemo.

Of course, Sophie is best known for her hit 'Shopaholic' series, which follows a retail-obsessed financial journalist -- and later hit the big screen as "Confessions of a Shopaholic," starring Isla Fisher.

Her most recent book, "What Does It Feel Like?," dropped last year and was inspired by her own cancer journey.

She was 55.