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Meanwhile, the ambitious Sorghaghtani had secretly teamed up with Güyük's cousin Batu Khan, the senior male in the Borjigin and ruler of the Golden Horde (north of Caspian Sea to Bulgaria). In 1248, when Güyük was setting out on a campaign to the Middle East (ostensibly for conquest, but possibly to defeat Batu Khan), he died under somewhat suspicious circumstances; some have speculated that Sorghaghtani may have taken "direct action against Güyük".