It seems like overnight, singer, Justin Bieber, went from a teen who posted covers on YouTube to a global sensation and hit-producing machine. The singer has certainly enjoyed the luxuries of his music career, and, of course, has the smash hits and a dedicated fan-base who keep coming back for more to show for it.

But many have noticed how unwell the singer had looked recently, and now he has revealed the reason why.

Keep scrolling for the full story.

Justin Bieber has been in the spotlight for quite some time now.

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After laying the foundations for his singing career by uploading covers to YouTube, the star was discovered at the tender age of thirteen by talent manager, Scooter Braun.

Despite his lavish life, Biebs actually comes from very humble beginnings.

Born on March 1, 1994, in Stratford, Ontario, Canada, to a single mother, Bieber was completely unknown on the music scene until he started uploading singing covers online.

But his life changed when he signed with RBMG Records in 2008.

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And in the 2 years that followed, the teen went from unknown to rubbing shoulders with some of the biggest A-listers on the scene.

In his early days, he quickly was hailed as a teen heartthrob.

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Bieber bulldozed into the Billboard Top 10 in early 2010 with his hit single “Baby," which also featured rapper, Ludacris - and teenage girls went crazy for it.

And since, there truly has been no stopping the star.

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His chart-topping success is unbelievable and seen him enjoy a life most could only dream of.

He has delivered hit after hit.

The likes of "Where Are Ü Now," "Sorry," "Despacito," and "Love Yourself," have all be extremely well-received.

Of course, he's also known for his public romance with now-wife, Hailey Bieber.

After first crossing paths in 2009, they got together officially 3 years later.

Recently, they got hitched.

Their wedding looked truly jealousy-inducing.

There's no denying how much Justin has changed throughout his career...

Having grown up in the spotlight, he had to live out his teenage years in the public eye - the good and the bad. In fact, he's recently admitted that his quick climb to fame left him "suicidal" - read more about what he candidly spoke about at the end.

We've watched his appearance take some dramatic changes.

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The classic Justin Bieber swoop hairdo is nothing but a distant memory now.

Recently, however, fans have noticed some worrying changes.

Many noted how unwell the singer has been looking recently.

In fact, many even speculated he had a drug problem.

His change in appearance led some people to believe he may have been using hard drugs after pictures surfaced of him looking ill with blotchy skin.

The singer has previously admitted to drug use and the effects it had on his mental health.

So it's understandable that fans may have jumped to this conclusion. Read more about his drug use at the end.

But this week, the singer took to Instagram to put the rumors to rest.

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And he revealed something pretty shocking about why he appears to look unwell.

Fans have had some strong reactions, to say the last.

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People flocked to social media to react to his shocking diagnosis. Keep scrolling for all the details on his diagnosis.

Some pointed out how they had previously been concerned for his health.

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His sickly appearance had clearly worried fans. Now, we finally have an explanation...

But some fans were completely devastated by the news.

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Take this user, for instance.

Some shared their own experiences.

Fans were offering their own words of encouragement for the star.

Many fans have been spurring the singer on.

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"Keep going brother."

And of course, several tweeted Hailey Bieber following the news.

We're sure she'll be right by her beau's side.

The singer's comments were filled with well-wishes.

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People urged him to stay positive.

Fans were understandably worried...

"my heart literally skipped several beats."

And many clapped back at those who were slamming the star for his appearance.

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You really don't know what is going on behind closed doors.

It's safe to say that his fanbase are right behind him.

Keep scrolling for what the star had to say about his health.

In an Instagram post, the singer revealed he has an incurable health condition.

Keep scrolling to learn more about his diagnosis.

"It's been a rough couple years."

The hitmaker opened up about his struggles with his health, acknowledging that he was aware of the speculation surrounding his wellbeing.

The singer then revealed he has been diagnosed with Lyme disease, a serious bacterial infection caused by ticks.

"While a lot of people kept saying Justin Bieber looks like s**t, on m*** etc. they failed to realize I've been recently diagnosed with Lyme disease." In some cases, Lyme disease can cause serious long term symptoms including nerve and heart problems and trouble with memory or concentration. And that's not all...

As well as being diagnosed with Lyme, Bieber revealed yet another shocking detail about his health...

"Not only that but had a serious case of chronic mono which affected my, skin, brain function, energy, and overall health."

The singer explained that he'll be opening up further in an upcoming documentary.

"These things will be explained further in a docu-series I'm putting on YouTube shortly... you can learn all that I've been battling and OVERCOMING!!"

But thankfully, the star has reassured fans he's getting the right treatment.

Bieber recently revealed that his rise to fame caused him to feel "suicidal." Keep scrolling to learn more about what the star honestly and openly admitted about his stardom. It's really shocking...