Complex sentence: His godfather was King George VI and the then-Princess Elizabeth (the future Elizabeth II) of the United Kingdom, who is his third cousin, as are the former King of Greece, and the former King of Romania.
Split into simpler sentences: His godfather was King George VI and the then-Princess Elizabeth (the future Elizabeth II). The Queen of the United Kingdom is his third cousin, as are the former King of Greece, and the former King of Romania.