In the caption, the pop superstar star addressed previous rumors about his appearance by explaining that his poor health had caused the changes people had noticed.
"While a lot of people kept saying Justin Bieber looks like sh*t, on meth etc. they failed to realize I've been recently diagnosed with Lyme disease, not only that but had a serious case of chronic mono which affected my, skin, brain function, energy, and overall health," he wrote.
Justin added that he'd be sharing more details about his health in an upcoming documentary series that he'll upload to YouTube. He didn't disclose a release date for the videos but said that they'd be released "shortly."
The caption accompanied a screenshot of a TMZ article that reported Justin's health news, which included a photo of the "Sorry" singer sitting in a car while wearing a black beanie and a gray patterned shirt.
The post attracted close to a million likes within an hour and more than 24,000 Instagram users have commented on it. In the comments section, fans shared messages of support and some of those encouraging comments came from fellow celebrities.
"Adapt & overcome, nothing stops the king," wrote YouTube superstar Logan Paul.
"GOD IS THE GREATEST NO CAP," Chance The Rapper added.
But Justin's non-famous Instagram followers chimed in as well.
"We are with you always love, soon you will be good, we will pray for you, count on us for everything," a fan added
Others responded to the "haters" Justin referenced in the caption.
"People need to stop assuming extremely negative things about for their entertainment," a fourth fan wrote. "I am so happy for you! Stay strong!"
Near the end of his lengthy caption, Justin indicated that he was getting the health care he needs to treat his Lyme disease. He also admitted that the last couple of years had been rough but promised his fans that he'll be back and "better than ever."TMZ reports that sources who have seen the documentary have said that it will show Justin trying to grapple with baffling undiagnosed symptoms in 2019. According to the article, the singer's doctors only confirmed the Lyme disease diagnosis late last year.
Lyme disease is an incurable condition caused by tick bites. Some of its symptoms include rashes, headache, fever and fatigue, the CDC reports. It can harm some of the body's major organs if left untreated.