Complex sentence: After Anne Boleyn's beheading, Sir William continued to serve in the king's Privy chamber and attendant to His Majesty; serving the King's third wife, Jane Seymour, just as he had served Queen Anne.
Split into simpler sentences: After Anne Boleyn's beheading, Sir William continued to serve in the king's Privy Chamber and as an attendant to His Majesty. He served the King's third wife, Jane Seymour, just as he had served Queen Anne.