Complex sentence: According to William of Rubruck and a Muslim chronicle, one of Batu's brothers murdered or poisoned the Great Khan Güyük and Batu then killed the imperial envoy, though this account is not completely confirmed by other major sources.
Split into simpler sentences: According to William of Rubruck and a Muslim chronicle, Batu then killed the imperial envoy, and one of his brothers murdered or poisoned the Great Khan Güyük. But this account is not completely confirmed by other major sources.