I'm surprised. As I mentioned above, reigning monarchs don't usually attend other reigning monarchs coronations. The only exception was the queen of Tonga in 1953, as far as I know. But then, the Brits are the only ones left in Europe who have coronations, and I guess times change!
I remember reading about the Queen of Tonga at HLM's coronation. Methinks the lady was a force of nature.

Charles may be changing things up a bit.