Having heard how stuffy and boring the Grand Galloping Gala could be Luna hatched a plan to get out of it. For the entire week before the gala she made sure not to milk herself, making sure that she was as engorged as she could be. She used her size glamour to hide what she was doing from Celestia as she knew that if she found out she’d try and stop her.
As the days progressed it started to become increasingly uncomfortable but she held out knowing it would worth it. She didn’t want to have to deal with those snooty nobles.
As the night arrived she got changed into her dress and as she heard Celestia about to enter, she released her size glamour as well as finally let the pressure out. With the sudden swelling of her breasts and large volumes of milk, her dress stood no chance.
When Celestia saw this she didn’t know what annoyed her more the fact Luna had done this at the last moment to get out of the Gala or the fact she hadn’t thought of doing this to get out of it.
With her plan a success Luna left and went to Ponyville to head to Nature’s Bounty to spend a relaxing evening getting milked.