The sentence “Brutus, who claims to be an honorable man, stabbed Caesar” has a subordinated non-definite relative clause (who claims to be an honorable man). The notion of being an honorable man contrasts with the idea of stabbing someone, so if we want to paraphrase this sentence coordinating this ideas (instead of subordinating one to the other, we could say:
BRUTUS CLAIMS TO BE AN HONORABLE MAN, YET HE STABBED CAESAR.
In this case, que coordinating conjunction of contrast is YET.
