TOKYO (AP) — Japanese Princess Yuriko, the wife of wartime Emperor Hirohito's brother and the oldest member of the imperial family, has died after her health deteriorated recently, palace officials said. She was 101.

Yuriko died Friday at a Tokyo hospital, the Imperial Household Agency said. It did not announce the cause of death.

Born in 1923 as an aristocrat, Yuriko married at age 18 to Prince Mikasa, the younger brother of Hirohito and the great-uncle of current Emperor Naruhito, months before the start of World War II.

She has recounted living in a shelter with her husband and their baby daughter after their residence was burned down in the U.S. fire bombings of Tokyo in the final months of the war in 1945.

Yuriko raised five children and supported Mikasa's research into ancient Near Eastern history, while also serving her official duties and taking part in philanthropic activities, including promotion of maternal and child health. She outlived her husband and all three sons.

Her death reduces Japan's rapidly dwindling imperial family to 16 people, including four men, as the country faces the dilemma of how to maintain the royal family while conservatives in the governing party insist on retaining male-only succession.

The 1947 Imperial House Law, which largely preserves conservative prewar family values, allows only males to take the throne and forces female royal family members who marry commoners to lose their royal status.

The youngest male member of the imperial family, Prince Hisahito — the nephew of Emperor Naruhito — is currently the last heir apparent, posing a major problem for a system that doesn't allow empresses. The government is debating how to keep succession stable without relying on women.

Prime Minister Shigeru Ishiba, visiting South America to attend the Asia Pacific Economic Cooperation and Group of 20 summits, issued a statement expressing "heartfelt condolences."

Naruhito, Empress Masako and their daughter Aiko and other relatives visited the Mikasa residence to mourn Yuriko's death. The palace announced that the general public wishing to offer condolences can sign a book beginning Saturday.

Yuriko had lived a healthy life as a centenarian before suffering a stroke and pneumonia in March. She enjoyed exercise in the morning while watching a daily fitness program on television, the Imperial Household Agency says. She also continued to read multiple newspapers and magazines and enjoyed watching news and baseball on TV. On sunny days, she sat in the palace garden or was wheeled in her wheelchair.

Yuriko was hospitalized after her stroke and had been in and out of intensive care since then. Her overall condition deteriorated over the past week, the Imperial Household Agency said.