By all accounts, Prince Philip was quite bright and also something of an intellectual. His grandmother, Victoria, was major influence on him growing up, and she had a reputation for being very intelligent as well as intellectual.
There is a difference. I think that William is bright but not particularly interested in the life of the mind, so not intellectual. I think the same is true of the late Queen. I think Philip and Charles, for all their differences, are similar in being bright and also having intellectual interests.