The words king and queen are common nouns. We use these words to talk about a person who rules in a country. Common nouns are not capitalized.
England used to have a queen, but now a king rules the country.
It is proper etiquette to kneel before a king or queen.
If the words king and queen are used as part of a name, then they must be capitalized.
The new monarch in England is King Charles.
His mother was Queen Elizabeth.
Capitalize the words king and queen only when they are part of a name.
▶It’s your turn. Decide if the words king or queen should be capitalized in this sentence: At formal events, a king wears a crown. Did you figure out that there is no name in this sentence? Therefore, nothing was capitalized.