Akihito, 86, underwent tests after he lost consciousness and his condition was being monitored, said the spokesman at the Imperial Household Agency, which manages the Japanese imperial family’s affairs.

He declined to give further details.

Akihito, now formally known as Emperor Emeritus, had breakfast as normal on Thursday, Kyodo news agency said. He has had heart surgery and has been treated for prostate cancer.

After three decades as emperor, Akihito stepped down in April in Japan’s first abdication in some 200 years and his son, Naruhito, became emperor.

Akihito’s 85-year-old wife, Empress Emerita Michiko, had surgery for early stage breast cancer in September.

The popular Akihito was the first monarch to take the Chrysanthemum Throne under a post-war constitution that defines the emperor as a symbol of the people without political power.

He said in a televised address in 2016 that he feared his age would make it hard for him to carry out his duties fully.