Complex sentence: His younger half-brother, Harald Sigurdsson, was also present at the battle and would in 1047 go on to become King of Norway, only to die in a failed invasion of England in the Battle of Stamford Bridge in 1066.
Split into simpler sentences: His younger half-brother, Harald Sigurdsson, was also present at the battle. He became King of Norway in 1047, only to die in a failed invasion of England at the Battle of Stamford Bridge in 1066.