Guan Yu slays Cai Yang

In the novel, Guan Yu finally met Zhang Fei at Gucheng after crossing through five passes and slaying six of Cao Cao’s generals. Zhang Fei was initially suspicious of Guan Yu, believing that Guan Yu had broken his oath and joined Cao Cao. At that moment, a group of Cao Cao’s soldiers led by Cai Yang arrived after pursuing Guan Yu. To prove his loyalty, Guan Yu slew Cai Yang and regained Zhang Fei’s trust.

What happened historically?

 * Historically, Cai Yang was killed at Runan during the Battle of Guandu