A mistress of North Korean leader Kim Jong Il (search) — whose son with him is considered a possible successor — has died of an illness, according to media reports.

Little is known about Ko Young Hui (search), in keeping with the secrecy that shrouds one of the world's most reclusive countries. She emigrated to North Korea in the 1960s from Japan, where she had lived among the ethnic Korean minority.

South Korea's Yonhap news agency said Ko has had an operation for breast cancer and that Western doctors have treated her. An unconfirmed Japanese news report said in October 2003 that Ko was hospitalized after she was badly injured in a car crash.

South Korean officials have said they are trying to confirm Ko's death, which Japanese media also reported, citing unidentified sources.

Ko, 51, reportedly enamored Kim while working as a folk dancer. Her son, Jong Chol, once studied in a Swiss school and is believed to be have worked at the propaganda department of the North's ruling Workers' Party of Korea (search).

North Korean experts have speculated that Kim considers Jong Chol as a possible successor, just as Kim inherited power from his father and national founder, Kim Song Il, who died in 1994.

Kim also has an older son, Jong Nam, by a different mother. But Jong Nam embarrassed Pyongyang in 2001 when he was caught trying to enter Japan on a fake passport. He told Japanese officials he had intended to go to Tokyo Disneyland.

Confucianism favors the eldest son as heir. But ancient Korean courts were rife with power struggles among sons and mothers. Palace coups and bloodbaths were common.

North Korea watchers say Jong Nam was a spoiled, ill-mannered child, known for bingeing sprees at a Pyongyang hotel and shopping excursions to China. When he was detained in Tokyo, the chubby, bespectacled man was sporting a diamond-encrusted Rolex watch and carrying wads of cash.

Jong Nam's mother, Sung Hae Rim, was a former actress forced to divorce her first husband and marry Kim. After years of estrangement, she is believed to have died in exile in Moscow last year.

Kim Jong Il is believed to have married three times. Ko has been described as both a wife and a mistress.