 The truce of <unk> did not last long , and in the spring of 1651 Khmelnytsky 's Cossacks begun advancing west again . On June 1 , 1651 Wiśniowiecki brought his private army to face the Cossacks in <unk> . He commanded the left wing of the Polish @-@ Lithuanian army in the victorious Battle of <unk> on 28 – 30 June . The Polish @-@ Lithuanian army advanced after the retreating Cossacks , but on July 17 the King " left the whole army to Potocki ... and having given the order that the army march into Ukraine , the King himself parted ... to Warsaw to celebrate his victories over the Cossacks . " Later that year , on 14 August , Wiśniowiecki suddenly fell ill while in a camp near the village of <unk> , and died on August 20 , 1651 , at the age of only 39 . His cause of death was never known , while some ( even contemporaries ) speculated he was poisoned , but no conclusive evidence to support such a claim have ever been found . Based on sparse descriptions of his illness and subsequent investigations , some medical historians suggest the cause of death might have been a disease related to cholera . However , one account states , " following a cheerful conversation with other officers who had congregated for a military council in his tent on Sunday , 13 August <unk> he had eaten some <unk> with <unk> and washed them down with <unk> , and from that contracted <unk> . After lying ill for a week , he died there , at <unk> " . He was given a " ceremonial funeral with the entire army present . On August 22 , Wiśniowiecki 's body was seen off with the <unk> <unk> on its journey to his residence " . 
