Tournament rules question

[TheMainEvent]

Let's say player A limps in, player B goes all-in for the size of the big blind, player C who is friends with player B checks in the BB. C flops trips and checks all the way down. A and B turn their hands up and C realizes that his friend B has A beat, but is still losing to his trips. Can player C muck his cards, pretending he has the losing hand? Or is he forced to turn it up even if no one requests to see it?