Prince Mikasa, the 100-year-old uncle of Emperor Akihito and the oldest member of the Imperial family, died of cardiac arrest at a Tokyo hospital on Thursday, the Imperial Household Agency said.
Mikasa was the youngest brother of Emperor Hirohito, the present Emperor's father and was known as a scholar of ancient Asian history. He served as honorary president of the Middle Eastern Culture Center in Japan and the Japan-Turkey Society.
The prince was the only living member of the Imperial family who had a military experience.
According to Imperial Household Agency sources, the prince had steadily recovered and was in good health after his surgery in 2012. But, recently he had been unwell after being hospitalized at St. Luke's International Hospital for acute pneumonia in mid-May.
The sources said Mikasa had recovered from the symptoms but his heart function had weakened due to old age.
Prince Mikasa was the fifth in line to the Chrysanthemum Throne and his death left the Imperial family with only four males among its remaining 19 members. His death also revives the question of whether women should be allowed to inherit the throne breaking the tradition of only-male succession.
In August, the 82-year-old Emperor Akihito hinted that he wanted to step down. However, it is not possible under the current law as the step is unprecedented in modern Japan.
The remaining four male heirs include Akihito's 80-year-old brother, two middle-aged sons of Akihito including Crown Prince Naruhito and 10-year-old Prince Hisahito, the emperor's only grandson.
On Thursday morning, Prime Minister Shinzo Abe expressed his condolences over the Prince Mikasa's death.
"Prince Mikasa supported his elder brother (Emperor Hirohito) as well as the current Emperor, contributing to the peace of the country and the welfare of its people," Abe said in a statement read by Chief Cabinet Secretary Yoshihide Suga at a news conference on Thursday morning.
Prince Mikasa was born as Prince Takahito and the fourth son of Emperor Taisho on Dec. 2, 1915.