"Jeff? How did you... How are you so small? And why were you in my undies?"
Jeff, unaware of what to say, stutters out "I-I don't know! I was sitting on m-my bed, and then suddenly appeared in there!", silently praising himself for his last-minute lie. It was partially true though.
"Alright then... Although, I can't let you run around at this size! You're so small, you could get stepped on! Though, where should I keep you..."
After thinking for a moment, Diana decides that the best course of action would be to just keep him with her, for protection from being stomped. So, she pulls her skirt back up, pulls her panties out along with the waistband of her diaper, and drops him in there, making sure to be gentle enough to not hurt him.
================ Jeff POV ================
After being dropped into her diaper, Jeff is left in darkness. However, he's back where he had intended to sit, only with Diana's knowledge of him being there. He was glad that she had mercy, and was too innocent to think anything more of it.
Jeff now had full movement within her diaper, and could very easily mess with her still...