The nihilist in denial that he is a nihilist

Can you be a nihilist without realising it?

Yes, because even if you declare yourself to be a principled man, you may in practice not follow or defend any principle, not even that of submitting to Truth, Logic and Morality, which is the minimum standard of any atheist claiming to be moral and rational.  

You could pretend to be an adherent of any religion but not defend any religious principle at all.  

You could be the Pope or the Archbishop of Canterbury and still be a nihilist, if there is no principle at all that you would  defend and you have no principle at all that you care to state.