I've never believed Charles would be king, or if he was it would be on agreement that it would be for a very short period. He's so yesterday, whereas Wills & Kate are like a breath of fresh air.
Bit of a shame for him as he's waited so long, but I think it would be the nail in the coffin for the Royals if he and Camilla were in (as Diana once put it) the "top job." What do you think?
Given his age (65), I doubt Charles will ever be king. The way his mother is going I can't see her popping her clogs any time soon, and also she has said that she will ever abdicate the throne. I think the best Charles can hope for is to be appointed as Prince Regent should she become too old or infirm to carry out her royal duties.
Just for the record, William IV (the uncle of Queen Victoria) was the oldest heir to succeed to the British throne, at the age of 64, and his reign lasted for 7 years. He had no legitimate heirs and was survived by eight of his ten illegitimate children, all by his bidie-in, an actress called Dorothea Jordan, which is why the crown passed to his niece.