SEOUL (AFP) - The second wife of North Korea's founder Kim Il Sung - the step-grandmother of Pyongyang's current leader Kim Jong Un - has died, the South's government said on Wednesday (Dec 12).

Ms Kim Song Ae, who was born in 1924, is said to have been sidelined in a power struggle decades ago and put under house arrest after failing to promote her own son Pyong Il - now the North's ambassador to the Czech Republic - as the founder's heir.

"We are going to update our Who's Who of North Korea by factoring in her death," a spokesman at Seoul's Unification Ministry said, without saying when she had died or giving any further details.

Ms Kim Song Ae reportedly married North Korea's founder and leader Kim Il Sung in 1953, four years after the death of his first wife Kim Jong Suk - the mother of his successor Kim Jong Il and grandmother of the incumbent.

She was seen standing alongside her husband greeting former US president Jimmy Carter when he visited Pyongyang in 1994 during the first crisis over its nuclear development.

This is not the first time reports of her death have emerged.

In 2014, North Korean Intellectuals' Solidarity, a group of North Korean defectors in the South, said she had died in Kanggye, where she had been living incommunicado.

The North is highly secretive and the last time she was mentioned by its state media was in 1995, when she was listed as a mourner at the funeral of former defence minister O Jin U.

Ms Kim had another son and a daughter. Her second son, Kim Yong Il, died in Germany in 2000, aged 45, while the daughter lives in Austria with her husband, according to the South's Yonhap news agency.