Question: Wilhelmine Schröder was the royal mistress of a man that was King of Sweden beginning in what year?
Sentence (from "Charles XV of Sweden"): Charles XV & IV also Carl ("Carl Ludvig Eugen"); Swedish: "Karl XV" and Norwegian: "Karl IV" (3 May 1826 – 18 September 1872) was King of Sweden ("Charles XV") and Norway ("Charles IV") from 1859 until his death.
Relevant evidence: Yes