Image imported from derpibooru 
Original Description:
 
After a long day of ruling the kingdom &/or a night at the gala, Celestia strips off her dress & keeps her slightly wet diaper on & has a nice relaxing shower. As she soaks herself, her diaper begins to absorb the water & make it swell up which intrigues the princess as she touches it. She becomes quite fascinated with how squishy it feels & starts rubbing herself with it & she enjoys it so much, she moaning pleasurably & musically & eventually reaches orgasm.