Complex sentence: Prince Prajadhipok was the youngest of nine children born to the couple, but overall he was the King's second-youngest child (of a total of 77), and the 33rd and youngest of Chulalongkorn's sons.
Split into simpler sentences: Prince Prajadhipok was the youngest of nine children born to the couple. Overall he was the king's second-youngest child (of a total of 77), and the 33rd and youngest of Chulalongkorn's sons.