Oh it’s not true, I don’t wish harm upon you

From birth we’ve been like sisters, of different mothers, Within the spirit of the same womb

May the gods strike me down if I forsake you

Mater meus

You’re beautifully made and to you I’m forever grateful

I’ll never forget that you showed me to make art

And I know the love you showed me came from a pure and Noble Heart

I love you and if you want I’ll call you king

But why do I lie awake each night thinking

Instead of you, it should be me?

….

I always knew I could be the one

Though I feel the endless pain of being and I am scorched by

The sun

Of humble origins and born of a cursed race

My name is Brutus but the people will call me Rex

(edited lyrics from buttress’ brutus)

so at first when I heard this song I thought of Luna, but listening again I really think it fits Sunset more, especially her story in the comics where she demands Celestia makes her a princess.