Frank Underwood was murdered.
Netflix booted Kevin Spacey off his own series last year after it was revealed that he has sexually assaulted a number of different men. Spacey was one of the first men taken down by the Me Too movement, and his career will likely never recover. House of Cards was Netflix's first original series, and so they weren't about to just cancel the show before wrapping up the story. A final season was planned, and it has finally arrived.
Spacey's on-screen wife, played by Robin Wright, takes control of the presidency after he is killed off. Although fans knew Spacey's character (Frank) would be axed, nobody knew how. Now that the series has finally arrived, the cause of his death has been revealed. Only keep reading you if you don't mind spoilers or have finished the series!
Michael Kelly's character Dough admits that he murdered Frank to his wife, Claire. Apparently, Frank was on his way to kill his own wife, and Dough decided to stop him. He found a way to toy with Frank's medication, causing him to overdose and die in his sleep. Claire kills Doug after the revelation, which means no one will ever find out that the president was assassinated by his closest ally.