Read the full text of Cymbeline Act 5 Scene 3 with a side-by-side translation HERE.
Posthumus runs into a couple of British lords who had fled from the fight. He tells them what happened in the battle.
The lords find it strange that an old man and two boys could save the day.
Posthumus is in a really bad mood and makes fun of them by coming up with a little riddle about the battle. Real mature.
Not really understanding what's happening, the lords just figure that Posthumus is really angry, though they can't understand why.
Once the lords leave, Posthumus gets rid of his British clothes and puts his Roman uniform on again. Huh?
Posthumus wants to punish himself for Imogen's death by dying himself.
Two captains enter and declare how grateful everyone is for the four men who saved the day. Aside from the old man and two young boys, there was another man in "silly habit" (translation: weird clothes). That fourth man would be Posthumus.
Now that the war's over, no one can find any of the men.
The captains find Posthumus and see that he is a Roman. They decide to take him to the king for punishment.