The story is about two people - both leaders of their respective species. On one side, the tall, powerful looking male character, and a young, beautiful queen, who he is in love with. After being rejected, he invades her world - a beautiful ring world, with its sun in the center. After the world is evacuated he lands his craft near her palace, and at the same time she takes off her necklace, which is a replica of her world, and takes the sun out of the middle, which causes the real sun to die, and the world starts to freeze.
The film ends with the two of them standing in front of each other - they embrace, and die in each other's arms as the ice reaches them.
I also remember that it had a brilliant, moving soundtrack.
A little more information: This was an animated short, which I came across on the internet, and it would have been 5 years ago at least.