The song is from season 5 episode 24 of MLP:FiM.
♫ Lyrics for the song:
( You can support the show here: https://itunes.apple.com/us/tv-season/my-little-pony-friendship/id975102612 )
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[Coloratura]

I'm here to show you who I am
Threw off the veil, it's finally time
There's more to me than glitz and glam, oh-whoa
And now I feel my stars align

For I had believed what I was sold
I did all the things that I was told
But all that has changed, and now I'm bold
'Cause I know

That I am just a pony
I make mistakes from time to time
But now I know the real me
And put my heart out on the line

And let the magic in my heart stay true
Whoa-whoa-whoa-whoa
And let the magic in my heart stay true
Whoa-whoa-whoa-whoa
Just like the magic inside of you

And now I see those colors
Right before my eyes
I hear my voice so clearly
And I know that it is right

They thought I was weak, but I am strong
They sold me the world, but they were wrong
And now that I'm back, I still belong
'Cause I know

That I am just a pony
I make mistakes from time to time
But now I know the real me
And put my heart out on the line

And let the magic in my heart stay true
Whoa-whoa-whoa-whoa
And let the magic in my heart stay true
Whoa-whoa-whoa-whoa
Just like the magic inside of you

Just like the magic inside of you...

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"My Little Pony" is owned by Hasbro,
"MLP: Friendship is Magic" is created by Lauren Faust.