Robert Dudley? Bigamy? First I've heard of it. Yes, he had an affair with Douglas Sheffield - and fathered a son on her - but I don't think he ever committed bigamy. Amy Robsart was dead long before Robert married Lettice Knollys...
Sorry, I mispoke. His bastard son attempted to prove that Douglas and Dudley DID marry which would've made Bob Snr guilty of bigamy with Lettice