Shimmerstar takes her study over Astronomy very seriously even when studying abroad as Princess Luna found out who be a better teacher for the stars then the one who rules over the night time sky given her family name (much as she hates to use it now) and being a Alicorn it not too hard to get to see Luna the two get along very well with each other often makeing fun of their respective siblings behind close doors for fun one night as she was teaching her Shimmerstar gotten a idea to turn Luna into her diaper for the night so when her guard was down she use a diaper spell on her and once she was a diaper put her on before she could even react teaseing the moon princess she such a thick diaper as she has plan to take no breaks wanted to see if she can name all star constellations through the night without breaks so Luna will have to do this lesson as her diaper and likely as her diaper in future lessons it just he better hope she don't become too absorbed into her lesson that she forgets she even wearing Luna

Art made by  vitriolink