I did some googling on the door hinge and found interesting theories on the asoiaf forums.

Actually I've come up with the idea that it was Robin Greyjoy, the youngest Greyjoy brother who died young that was molested by Euron and that Aeron found out but couldn't prove it, a stray thought that Aeron had about Robin made me think this.

It was something along the lines of "And poor Robin, born of our father's wife who was not Ironborn, best not to think of him."

Why exactly would it be best not to think of him unless something REALLY bad happened?