This is the song "Celebrate The Magic", from Disneyworld's pre-castle show. Happily Ever After has replaced the Celebrate the Magic show as of May 12, 2017 at Magic Kingdom. This video will live on to keep the nostalgia going :) This content uses original recordings of the show, not source music. All content is Copyright © The Walt Disney Company. No copyright infringement intended.

I cleaned up audio taken from several videos of the castle show to make this soundtrack. It is, essentially, a "remix" of the original song. I had to cut out some parts that were instrumental Disney theme songs from assorted Disney films. If you want to use this in another video or an AMV, go ahead! I'd love it if you credit this video so more people can discover my original remix.

This song is sung by "Laura Cooksey" - here is her tweet from opening night:   / 268432579294818304   (Thanks jgrasshoff for posting this in the comments).

You can turn on subtitles for the lyrics, or read them here (Thanks DisneyBug for transcribing it):
Celebrate a world filled with magic
Wish upon a star that shines so bright
Enter a world of make believe
Let your dreams come true tonight!

Celebrate a world filled with magic
Where happiness is found around the bend, where all your dreams and fantasies, magically will never end!

Celebrate a world filled with magic
Wish upon a star that shines so bright
Enter a world of make believe

"I only hope that we never lose sight of one thing – that it was all started by a mouse."

Let your dreams come true tonight
Celebrate the Magic!

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Youtube tells me this has been watched for over 100 hours. Thank you for watching - let the Disney magic live on!