Elpia

She is the missing princess of Myfical
her mother ran away from the palace when she was just a baby ( have not thought of why)
and she was raised in a town near ponyville called Mareaton ( her mother died after 3 years )

after the Queen's disappearance her child hood friend Awedrop became the prime minster
he is a kind man but he has two evil twin children ( who want to remain in the life of luxury so when Elpia's Powers started to get the attetion of Luna and Celestia ( who have been looking for their god-mother ( Elipa's mother) but find Elpia instead; but Elpia runs away and meets Benmaru who talks her into accepting her role as Princess but in return she makes him promise to go with her
but the daughter tries to steal the throne and when that plan fails and then the son uses dark magic to make Elpia's heart belong to him ( kind of like the spell used on Draculura in "Why DO Ghouls Fall in Love" ) but the spell ends of broken when Benmaru confesses he loves her

info on the "Hope Power"
( all the princess have a special power unique to their cutie mark ( Somewhat) much like with luna and Celestia the powers of hope were passed down )
( here is a quick back-story ( it ties to luna and Celestia ) a long time ago the Solar and Lunar kingdoms were at war
but the youngest prince of the Solar kingdom and the youngest of the Lunar Kingdom were deeply in love but were forced apart by their families as hatred grew so did the love the two shared and when war was on the rise a Queen of Hope rose and gave up her magic to untie the two lovers by giving them the (true ) powers of their fore fathers. they became King Sol and Queen Crescent and untied the two kingdoms together.