I think Charles has been unwell for some time, I've commented this on other threads but my Dad has got rheumatoid arthritis and I've often thought Charles has the same. It's a very cruel condition and the drug treatments are fairly toxic. They work by dampening down the immune system, and grief is known to have a similar effect so he may be especially vulnerable right now. This is going to be a hard day for them all, apart from Harry and Andrew who will no doubt parade themselves like babboons on steroids.