Lee, who was born in 1922, had served as Chair of the Kim Dae Jung Peace Centre, which was founded by the former President to promote inter-Korean reconciliation and fight global poverty, Efe news reported.
Lee accompanied her husband Kim -- who served as President for five years from 1998 -- to Pyongyang in 2000 for the first inter-Korean summit with then top leader of North Korea Kim Jong Il, father of the current leader Kim Jong-un.
South Korean President Moon Jae-in posted a message from Finland, saying he regrets that he could not take Lee to Pyongyang when he visited there in 2018. He said he believes Lee will support him from heaven to achieve peace.
Inter-Korean relations are at a standstill after the second summit between the North and the US ended without agreement in February.
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