The explanation of these events is reserved for the last act, which discovers Carlos in a dungeon, into which the Marquis enters. Though the unfortunate youth can no longer doubt the perfidy of his friend, he does not dream of reproaching him for an act he is convinced sprang from necessity, but only regrets that the queen should have been involved in his destruction. Convinced that both are victims deliberately sacrificed, his surprise is extreme when Posa gives him again the queen's letter that he had committed to his safe keeping, and had imagined in the hands of Philip. An eclaircissement ensues; in the midst of which Duke Alba enters to announce his freedom, and apologize on the part of the king for the mistake that led to his imprisonment. The prince refuses to take back his sword, or leave the dungeon till his father comes in person to restore him to liberty. Alba departs with this message to the king, and the Marquis, exulting in the success of his scheme, explains fully all his past conduct. He has seemed to be the prince's enemy only that he may serve him better. When deceived by Count Lerma's officious representations, Carlos had thrown himself at the feet of the princess of Eboli, and Posa had arrived too late to prevent a confession, which in the hands of that envious woman might ruin all, the Marquis had suddenly resolved upon a bold manœuvre. This was no less than to divert the king's suspicions to himself, and thereby secure time for the prince's escape to Brabant. For this purpose he wrote the letter to the Prince of Orange, stating that he (the Marquis) was in love with the queen; that he sought to fix the sovereign's suspicion upon his son, who was not only innocent of the offence, but had endeavored, through the princess of Eboli, to warn his mother-in-law against the arts of Posa. This letter, as the writer intended, was intercepted by Taxis, and carried to the king; and, in consequence, the prince was restored to favor. The Marquis implores the prince to escape into Flanders, where his duty lies; Carlos refuses to leave him; at the same instant a shot is heard through the prison door, and the gallant Posa falls and expires. The king and nobles enter; Philip offers to embrace his son, who repels him indignantly, and discloses the fact that Posa was his friend. Here your approach is death—I'll not embrace you. (_to nobles_) Why stand ye thus embarrassed round? What deed Of horror have I done? Have I assailed The Lord's anointed? Fear ye nought. I lay No hand on him. Behold ye not the brand Upon his brow? Him God hath marked! None of the reproaches of Carlos are so bitter to his father, as his taunting allusions to the fraud practised upon the king by the deceased.