Justin Bieber has canceled his upcoming appearance at Madison Square Garden after announcing to his fans that he has been diagnosed with Ramsay Hunt syndrome.

He took to his Instagram page to explain why he had to push back the dates on his world tour. He talked about how Ramsay Hunt Syndrome has currently left half of his face paralyzed.

Ramsay Hunt Syndrome affects around five of every 100,000 people, caused by the same virus that causes chickenpox and shingles.

Dr. Helen Valsamis, chief of neurology at NYC Health + Hospitals/Kings County, explained that the virus stays dormant in the body when someone contracts chickenpox but can be reactivated in times of stress or when one’s immune system is compromised.

There are treatments available for this disorder, although it may take weeks to fully recover for the 28-year-old international popstar.