What son of Grand Duke Lithuania Kęstutis went on to defeat Švitrigaila and his Livonian allies?
Battle of Wilkomierz:  With the help of military units from the Kingdom of Poland, the forces of Grand Duke Sigismund Kęstutaitis soundly defeated Švitrigaila and his Livonian allies. Sigismund Kęstutaitis: Sigismund Kęstutaitis (Lithuanian: "Žygimantas I Kęstutaitis" ; Polish: "Zygmunt Kiejstutowicz" ; c. 1365 – 20 March 1440) was the Grand Duke of Lithuania from 1432 to 1440. Sigismund Kęstutaitis:  He was the son of the Grand Duke of Lithuania Kęstutis and his wife Birutė.
Sigismund Kęstutaitis