http://www.throneout.com/royal_scandal.htm
...basically says the allegation is gayness between a royal (obviously Charles) and a senior aide (Michael Fawcett, who was probably the gay rapist in the other story). It spices things up with the idea that Diana had proof, was going to use it in a custody battle, so the royals had her killed and have been bending the law to keep it all covered up.
I hope it's all true
