Would you think he may have wanted a girl for William to have a sister since he seems so close with his sister?
I don't think he gave any of it a lot of thought. He just wanted out as soon as the "spare" was born. He pretty much despised Diana at this point and was completely indifferent to the reality that cheating on a virgin teenager he had wed, throughout the marriage, would not only cause her excruciating pain; but also, in no small part, her subsequent acting out.