Princess Celestia was having so much fun playing sports that she didn’t take a bathroom break even when she had to pee pretty badly from all the water she drank to stay hydrated, and she ended up peeing herself. She was a little embarrassed but not overly so, and she was able to get over it pretty quickly. Even tell Twilight about it when the same thing happened to her.
 
Part of this is a test to see if the pee running down Twilight’s legs was the reason my last pony wetting pic wasn’t as popular and to see if just showing the wetness and no stream or pee running down her legs might be better received. And of course as with Twi I drew the outfit on her.