The Glowing Stone is a green crown-shaped gemstone and an item featured in the 2014 computer-animated family/fantasy film sequel The Swan Princess: A Royal Family Tale.
It is a powerful artifact which can destroy the Swan Princess. The legend states:
In a coming day, there will be a Swan Princess.
She will usher in an age of goodness.
And in her presence
Pure Evil will not survive.
Behold the Glowing Stone
Must be kept hidden.
For if Evil possesses it,
It will have the power to withstand
The presence of the Swan Princess
And destroy her.
In the movie, the Glowing Stone was hidden by a flying squirrel in it cave named Squirly (called by Odette). When Odette touches the silver box, the evil force known as the Forbidden Arts notice it. So he notice that Odette is the Swan Princess by only touching the box. So with the help of the flying Squirls they tried to keep it save so the Evil Force would not hurt Odette. But then the Evil Force had it and sends off to destroy the Swan Princess on his own. The Glowing Stone was destroyed and later the Forbidden Arts was no more.