The "Sk8r Boi" singer came forward with her own diagnosis of the tick-borne illness back in 2015, and has since become something of a spokesperson for people suffering from the disease.
So when Justin announced he had the illness, Avril was among the first to respond - offering her help in any way she can.
"Today @JustinBieber shared that he has Lyme disease. There are too many people that have this debilitating disease!" she began. "People I love and care about and many friends and fans I have crossed paths with. To everyone affected by Lyme, I want to tell you that there is HOPE. Because Lyme is a daily struggle, for the better part of two years, I was really sick and fighting for my life...".
Avril continued: "I never want others to suffer the way that I did, and because of that it is now my mission to raise awareness & funds that will help eradicate this life-altering disease. Portions of proceeds from every show on the rest of the #HeadAboveWater tour and merch sales will continue to go directly to Lyme disease. I will continue to fight and to support!".
Following his announcement, Justin was trolled by numerous people, but didn't let the haters get him down as he tweeted that he was focusing on the good in his life.
"I see a lot of people on here just creating lies and saying that they hope I lose in everything I do," he tweeted. "Well I hope you all win. I hope everything you want in life happens for you. Regardless of how you feel about me I send back love."