Or maybe the duke also turned into a child and now they can get engaged since hes having difficulty getting rid of the curse
https://newtoki95.com/webtoon/12369499?stx=%EC%97%AC%EC%A3%BC%EC%97%90%EA%B2%8C+%EB%B2%84%EB%A0%A4%EC%A7%84+%EC%95%85%EB%8B%B9%EC%9D%84+%EA%B5%AC%ED%95%98%EB%8A%94+%EB%B0%A9%EB%B2%95&toon=%EC%9D%BC%EB%B0%98%EC%9B%B9%ED%88%B0
AYO WTF WHY ARE MY GUESSES LELSLSKD
AYO BIG BRAIN
Or maybe the duke also turned into a child and now they can get engaged since hes having difficulty getting rid of the curse