I follow a Facebook Duolingo group and a Polish speaking person learning English shared an error they felt was incorrect. The sentence was ‘the Prince is getting excited’ and they wrote ‘the Prince’s getting excited’. They were marked wrong for their answer and I agreed it was grammatically wrong because it just sounds wrong in English. But I can’t find an explanation why?

I follow a Facebook Duolingo group and a Polish speaking person learning English shared an error they felt was incorrect. The sentence was ‘the Prince is getting excited’ and they wrote ‘the Prince’s getting excited’. They were marked wrong for their answer and I agreed it was grammatically wrong because it just sounds wrong in English. But I can’t find an explanation for why this should be.