Complex sentence: Gideon's existence is inconsistent with Carl Barks's view of Scrooge as presented in "The Old Castle's Secret", wherein Scrooge states that he is the last of the Clan McDuck.
Split into simpler sentences: Gideon's existence is inconsistent with Carl Barks's view of Scrooge as presented in "The Old Castle's Secret". In this story, Scrooge states that he is the last of the Clan McDuck.