Kim Kyong Hui, 67, a senior party secretary, is the wife of the recently executed Jang Song Thaek, Kim Jong Un's uncle and former mentor.
She visited Russia last year for medical treatment and was in Singapore in 2010 for medical reasons, as well, the official told South Korea's Yonhap News Agency.
She was last seen in public on Sept. 9 when she watched a military performance.
Kim Kyong Hui has been absent from key anniversary events following last month's execution of her husband, who was accused of treason.
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