Complex sentence: John Harris, who would have been aged 10 years at the time of the alleged incident, did not claim to have been a witness to it, additionally, he stated that he had not heard the story of Webb Ellis' creation of the game.
Split into simpler sentences: John Harris, who would have been aged 10 years at the time of the alleged incident, did not claim to have been a witness to it. Additionally, he stated that he had not heard the story of Webb Ellis's creation of the game.