In rape trials, defence lawyers are banned from cross-examining an alleged victim about their sexual behaviour or history to protect them from humiliating treatment.
But there can be exceptional reasons to ditch that rule in the interests of a fair trial. The Court of Appeal said Mr Evans's case was one of those very rare exceptions.
It said that two other men who had sex with the woman had described their encounters with her in highly specific terms that were virtually indistinguishable from Mr Evans's own account of what had happened.
One of the encounters occurred days before the alleged rape - and the other in the days that followed.
On each occasion the woman had been drinking heavily and the sex occurred in a very specific way - including the words she used to encourage her partner.
Each time she woke up saying she had no memory of what had happened.
Lady Justice Hallett, one of the country's top judges, said that these events were so similar to what Mr Evans had described that a jury had to hear about them before deciding whether the woman had been incapable of giving her consent.