Long Live the King!
The King has disappeared! With their ruler lost and presumed dead, "Prince" Knight is next up for the throne. But at the coronation ceremony, Duke Duralumon slips a substance into the Queen's wine that will force her to tell the truth. Source: crunchyroll
Aired 17/09/1967EP 25 - Long Live the King!
Princess Knight
Princess Sapphire is a girl raised as a Prince. Through the mischief of an angel, the princess is born with both a girl's body and boy's mind. Since there is no boy successor in her kingdom, Sapphire is raised as a boy, but evil ministers try to reveal her secret. Unable to put up with the kind of vicious conduct prevailing in the kingdom, Sapphire disguises herself as "Princess Knight" and wields her sword of justice.
This is an animated version of the girls' manga featuring Sapphire's romance and adventure, which marked the first made-for-TV animated program geared towards girls in Japan.
(Source: Official site)