Which woman was the sister of XXX?
Prince Charles of Denmark
Between 1697 and 1699, there was a Danish policy to create an alliance with Sweden through a double wedding between Charles XII of Sweden and Princess Sophia Hedwig of Denmark, and Prince Charles of Denmark and Hedvig Sophia of Sweden (after the marriage of Hedvig Sophia of Sweden in 1698, she was replaced by Ulrika Eleonora of Sweden).
Princess Sophia Hedwig of Denmark