Prince Katsura, a cousin of Emperor Akihito and sixth in line to the Chrysanthemum Throne, died at a Tokyo hospital at 10:55 a.m. Sunday, the Imperial Household Agency announced. He was 66.

The prince had been rushed to University of Tokyo Hospital in a critical condition earlier Sunday, but died of acute heart failure, the agency said.

As the second son of Prince Mikasa, a 98-year-old uncle of the Emperor, Prince Katsura had been sixth in line to the throne. The death of the prince, who was not married and had no children, brings an end to his household.