The sun is brighter than she ever imagined.
When Luna returned, she came to Celestia first. Few words were said. Luna wanted revenge; Celestia accepted it.
She had never thought the sun to be so bright, so warm, so majestic.
So horrible.
Her plan is in motion. The Chosen Ones are on their way, searching for a power they already possess.
Celestia is well aware that they could very well fail. Luna might even kill them. Celestia would remain here forever, and she would welcome her fate.
Maybe then her heart would finally stop aching.