Question: What son of Grand Duke Lithuania Kęstutis went on to defeat Švitrigaila and his Livonian allies?
Sentence (from "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.
Relevant evidence: Yes