Task: Question Generation
Input (English):  Arbaces, King of Iberia, has been abroad, fighting in the wars, for many years; he returns home in triumph, bringing with him Tigranes, the defeated king of Armenia. He intends to marry his sister Panthea to Tigranes. Meanwhile, he learns that his mother, Arane, who hates him, has plotted his assassination. The regent Gobrius has foiled the plot. Tigranes' fiancee Spaconia accompanies him into exile, hoping to avert Arbaces' plans for the marriage alliance. Tigranes promises her he will remain faithful.
On his return Arbaces finds that he now has a powerful sexual attraction to his beautiful sister, the princess Panthea, whom he hasn't seen since childhood. Much of the play depicts his increasingly desperate struggle against his incestuous passion. Arbaces blames the protector Gobrius for his predicament; the minister had written Arbaces many letters during the king's years abroad, praising Panthea's beauty and her love for him. Panthea is also attracted to Arbaces, but her virtue restains them both. The king becomes so desperate that he decides to murder Gobrius, rape Panthea, and then commit suicide. Meanwhile, Tigranes too falls in love with Panthea, even though this means he breaks his faith with Spaconia. Tigranes exercises the self-discipline and rationality that Arbaces struggles to achieve, and rededicates himself to Spaconia.
Arbaces' dilemma is resolved when it is revealed that the situation is a complex hoax, staged by Arane and Gobrius to give an heir to the childless old king who was Arbaces' predecessor. Arane's plots against her supposed son were intended to restore the rightful succession. Arbaces is in fact Gobrius's son, and so Panthea is not actually his sister. Gobrius had plotted that his son would become the legitimate king, by marriage with Panthea; Arbaces does marry the princess, but steps down from the kingship.
Arbaces is presented as a mixed character, brave and formidable in battle, but boastful and somewhat vulgar. His character is explained by the trick of his birth: he cannot behave with the nobility of a king, because he isn't one by "blood." The comic relief in the play is provided by the cowardly Bessus and his cronies; their subplot turns on the customs of honorable duelling   and their comical violation. (Bessus was a well-known comic creation; Queen Henrietta Maria refers to Bessus in a 25 February 1643 letter to her husband, Charles I.)
A King and No King has a strong degree of commonality with the same authors' Thierry and Theodoret. The former might be regarded as the tragicomic version, and the latter the tragic, of the same story.
Output (English): Why did Gobrius plan that Arbaces would become the legitimate king?