Question: When did Eric Vi Of Denmark's mother die?
Answer: 29 September 1304

"Not to be confused with Agnes of Babenberg"
Agnes of Brandenburg (c. 1257 – 29 September 1304) was a Danish Queen consort by marriage to King Eric V of Denmark. As a widow, she served as the regent of Denmark for her son, King Eric VI, during his minority from 1286 until 1293