The story is set within a framing narrative told by a supporting character from The Prisoner of Zenda. The frame implies that the events related in both books took place in the late 1870s and early 1880s. This story commences three years after the conclusion of Zenda, and deals with the same fictional country somewhere in Germanic Middle Europe, the kingdom of Ruritania. Most of the same characters recur: Rudolf Elphberg, the dissolute absolute monarch of Ruritania; Rudolf Rassendyll, the English gentleman who had acted as his political decoy, being his distant cousin and look alike; Flavia, the princess, now queen; Rupert of Hentzau, the dashing well-born villain; Fritz von Tarlenheim, the loyal courtier.
Queen Flavia, dutifully but unhappily married to her cousin Rudolf V, writes to her true love Rudolf Rassendyll. The letter is carried by von Tarlenheim to be delivered by hand, but it is stolen by the exiled Rupert of Hentzau, who sees in it a chance to return to favour by informing the pathologically jealous and paranoid King. Rassendyll returns to Ruritania to aid the Queen, but is once more forced to impersonate the King after Rupert shoots Rudolf V. In turn, Rassendyll kills Rupert, but is assassinated in the hour of triumph by one of Rupert's henchmenâand thus is spared the crisis of conscience over whether or not to continue the royal deception for years. He is buried as the King in a state funeral, and Flavia reigns on alone, the last of the Elphberg dynasty.

Question: Who killed the king?
Answer: Rupert (Rupert of Hentzau)
Alternative answer: rupert of hentzau.