In 1248, Güyük demanded Batu come eastward to meet him, a move that some contemporaries regarded as a pretext for Batu's arrest. In compliance with the order, Batu approached, bringing a large army. When Güyük moved westwards, Tolui's widow and a sister of Batu's stepmother Sorghaghtani warned Batu that the Jochids might be his target. Güyük died on the way, in what is now Xinjiang, at about the age of 42. Although some modern historians believe that he died of natural causes because of deteriorating health, he may have succumbed to the combined effects of alcoholism and gout, or he may have been poisoned. William of Rubruck and a Muslim chronicler state that Batu killed the imperial envoy, and one of his brothers murdered the Great Khan Güyük, but these claims are not completely corroborated by other major sources. Güyük's widow Oghul Qaimish took over as regent, but she would be unable to keep the succession within her branch of the family.