a story to go along with sounds fun! Maybe a friend who sarcastically told you to work hard to grow your boobs since you are mildly jealous of her/their "big" DD cup breasts, who gets flabbergasted as she/they check in on you or encounter them and you somehow not only catch up, but get much, much bigger then them
(edit: also fun to mention little inconveniences/noticing changes, like "You accidentally knocked over your third coffee cup with your chest today. Either you should stop getting bigger or invest in one of those tumbler mugs that are all the rage.... better look into that mug then" or "Another shirt popped all its buttons as you were talking today. F for that top, it was super cute, but the ta-tas needed the room to breath!")