On 25 March 1252, Conrad IV of Germany and Elizabeth of Bavaria had a son, Conrad. When his father died two years later, the child became Duke of Swabia, King of Sicily, and King of Jerusalem.
Regents held Swabia for him. Jerusalem was managed by a relative in Cyprus. Sicily was handled by his father's half-brother Manfred, who usurped the throne for himself in 1258. The child, being raised by his uncle the Duke of Bavaria and called by the diminutive Conradin, didn't have the resources to hang onto Sicily.
Because of his tender age, Pope Alexander IV forbade him becoming Holy Roman Emperor—even though Hohenstaufens were Guelphs, supporting the authority of the pope over that of the Holy Roman Emperors—giving it instead to Alfonso X of Castile. His other royal titles were respected, however. The Guelphs of Florence invited him to come and re-take Sicily from Manfred, but his uncle refused the invitation since his ward was still a child. Manfred was killed by Charles I of Anjou, who then tried inserting himself further into Italian politics. Envoys from Italy were sent to Conradin, asking for his help against the Angevin incursion. Having just become a teenager, Conradin accepted the offer, crossed the Alps, and declared his intention to reclaim Sicily.
He received moral and military support from many quarters, and in July 1268 his fleet defeated that of Charles. In August, however, at the Battle of Tagliacozzo in central Italy, Charles proved a more clever commander and defeated Conradin's army of Italian, Spanish, Roman, Arab, and German troops. Conradin escaped capture, fleeing first to Rome and then to Astura, where the lord of Astura, Giovanni Frangipani, offered him refuge. Giovanni was not his friend, however; he turned Conradin over to Charles, who had him beheaded on 29 October 1268. He was the last Hohenstaufen, so with his death the dynasty ended.
What happened to his titles, since he left no heirs? Sicily was gone. Swabia was claimed by Frederick, the son of Conradin's Aunt Margaret on his father's side. (Frederick also "claimed" Sicily, but that was not going to achieve anything.)
The "Kingdom of Jerusalem" was a more complicated situation—as it always had been. Let's go there next time.