Read this: After Richard's death on 6 April 1199 there were two potential claimants to the Angevin throne: John, whose claim rested on being the sole surviving son of Henry II, and young Arthur I of Brittany, who held a claim as the son of John's elder brother Geoffrey. Richard appears to have started to recognise John as his heir presumptive in the final years before his death, but the matter was not clear-cut and medieval law gave little guidance as to how the competing claims should be decided. With Norman law favouring John as the only surviving son of Henry II and Angevin law favouring Arthur as the only son of Henry's elder son, the matter rapidly became an open conflict. John was supported by the bulk of the English and Norman nobility and was crowned at Westminster, backed by his mother, Eleanor. Arthur was supported by the majority of the Breton, Maine and Anjou nobles and received the support of Philip II, who remained committed to breaking up the Angevin territories on the continent. With Arthur's army pressing up the Loire valley towards Angers and Philip's forces moving down the valley towards Tours, John's continental empire was in danger of being cut in two.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): Who was the sole surviving son?
John