The younger brother of former Japanese Emperor Hirohito died Thursday at the age of 100.

The Imperial Household Agency announced that Prince Mikasa had died in the morning at a hospital in Tokyo.

Japanese media reports say he had been hospitalized since May, initially because of pneumonia. Citing unnamed sources, they say his condition took a sudden turn for the worse on Thursday.

Prince Mikasa was born on Dec. 2, 1915. He is the uncle of the current Emperor Akihito and was fifth in line to the throne.

His brother Hirohito reigned for more than 60 years, during World War II and until his death in 1989.