The Battle of Stiklestad  in 1030 is one of the most famous battles in the history of Norway. In this battle, King Olaf II of Norway  was killed. During the pontificate of Pope Alexander III, the Roman Catholic Church  declared Olaf a saint in 1164. His younger half-brother, Harald Hardrada, was also present at the battle. Harald was only fifteen when the battle of Stiklestad took place. He became King of Norway in 1047, only to die in a failed invasion of England at the Battle of Stamford Bridge in 1066. The authenticity of the battle as a historical event is subject to question. Contemporary sources say the king was murdered. According to the Anglo Saxon Chronicle of 1030, Olaf was killed by his own people. Adam of Bremen wrote in 1070 that Olaf was killed in an ambush, and so did Florence of Worcester in 1100. Those are the only contemporary sources that mention the death of the king. After the king's canonization it was felt that the saint could not have died in such circumstances.  The story of the Battle of Stiklestad as we know it gradually developed during the two centuries following the death of King Olaf. Saint Olaf must have fallen in a major battle for Christianity.

Based on the above article, answer a question. How many years old was Harald Hardrada when he died?
51