I was so surprised in the way that Dudley showed his affection to Harry like that. I think that maybe, deep down, he always had some sort of respect for him, but he didn't want to admit it. But when Harry saved his life, it grew. Also, Dudley most probably would never be seeing Harry again, so I guess he found it unusual as to the fact that they were going to be separated, other than when Harry returned to Hogwarts. I have to admit it though, I thought it would've been Aunt Petunia who showed some sort of affection towards Harry.
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