'Shopaholic' author Sophie Kinsella's warning signs ahead of brain cancer diagnosis: 'I was stumbling'

Sophie Kinsella, best known for her best-selling "Confessions of a Shopaholic" book series, is opening up about the unnerving warning signs she experienced ahead of her brain cancer diagnosis. 

During Tuesday's episode of "Good Morning America," the British author – whose real name is Madeleine Wickham – sat down with Robin Roberts to discuss the moments she realized "something really was wrong" with her body before discovering she had a brain tumor. 

"The first symptoms that I had was... my legs. I was stumbling...