Question: When did Engelbert, Count Of Nevers's mother die?
Answer: 21 June 1483

Elizabeth of Nevers (born: after 24 August 1439 in Nevers; died: 21 June 1483) was Duchess of Cleves from 1455 until her death, due to her marriage with John I of Cleves-Mark. She was the matriarch of the house of Cleves-Nevers, and thus the Cleves line of the Counts and dukes of Nevers. Because the territory was part of her inheritance, it fell to her son Engelbert after her death