Demi Lovato has warned bullies not to "f**k with" her sister.

The 22-year-old singer is an older half-sibling to 12-year-old actress Madison De La Garza [also known as Madison Lee and Maddie]. It emerged on Twitter that Madison suffers from scoliosis - a curvature of the spine - after Demi defended her from trolls.

"Physical disabilities are NOTHING to joke about. SEVERE SCOLIOSIS IS NOTHING TO MAKE FUN OF," the loyal star wrote.

"For anyone telling me to "chill".. The impact bullies have over the internet can lead people to suicide. I can handle the bulls**t. But do NOT f**k with my baby sister. I'm all for peace and spreading love UNTIL you go after a 12 YEAR OLD who did NOTHING to you.. So disappointed that after all the conversation about cyber bullying in this world that people would continue to do this to others. @Maddielovesyou1 you are BEAUTIFUL and the most precious little angel in my life and I will always protect you. I LOVE YOU. (sic)"

The musician's fans were quick to support her, assuring her that most of her followers are right behind her. They also helped to get the hashtags #MADISONISBEAUTIFUL and #FeelBetterMaddie trending.

Demi has had her own problems to deal with, and in 2010 she checked into rehab to deal with an eating disorder and problems with substance abuse. She's also had to handle bullying, and has been very vocal about her thoughts on the subject.

She's even described her personal struggles in book Staying Strong: 365 Days a Year.

"I was bullied when I was 12 years old. I'm not saying I was totally innocent - I had my bratty days! But at the end of the day, no one deserves to be bullied. I ended up leaving public school because the bullying got so bad. I just couldn't deal with it," she previously opened up to Seventeen magazine.