Princess Yuriko of Japan, the wife of Emperor Hirohito’s younger brother and the oldest member of the imperial family, has passed away at the age of 101, following a recent decline in her health, palace officials announced.

Yuriko died on Friday at a Tokyo hospital, according to the Imperial Household Agency. While the cause of death was not officially confirmed, Japanese media reports suggest she succumbed to pneumonia.

Born in 1923 into an aristocratic family, Yuriko married Prince Mikasa, the younger brother of Emperor Hirohito and the uncle of current Emperor Naruhito, when she was just 18, just months before the outbreak of World War II.

She later recounted living in a shelter with her husband and their infant daughter after their home was destroyed in the 1945 US firebombing raids over Tokyo. Throughout her life, Yuriko raised five children, supported her husband’s academic work on ancient Near Eastern history, and carried out her official duties, including numerous philanthropic efforts.

Yuriko outlived her husband and all three of her sons. Her passing reduces Japan’s shrinking imperial family to just 16 members, including four men, highlighting the challenges the country faces in maintaining the royal lineage. The issue of succession is particularly pressing, as the 1947 Imperial House Law mandates that only males can inherit the throne, and female royals who marry commoners lose their royal status.

The youngest male member of the imperial family, Prince Hisahito, the nephew of Emperor Naruhito, is currently the only heir apparent, but the lack of a clear male successor poses a dilemma for the monarchy. The government is grappling with how to ensure the continuity of the royal family without relying on female heirs.

Until recently, Yuriko had enjoyed relatively good health as a centenarian, maintaining an active lifestyle by exercising each morning while watching a fitness program on TV. She also kept up with current events, reading newspapers and magazines, and enjoyed watching news and baseball. On sunny days, she would sit in the palace garden or be wheeled out in her wheelchair.

After suffering a stroke and pneumonia in March, Yuriko had been in and out of intensive care. Her condition had worsened over the past week, leading to her death, the Imperial Household Agency said.