Short answers, pulled from the story.
The Admiralty was the British government department responsible for commanding the Royal Navy. It operated from the early 18th century until its abolition in 1964, when it was merged into the new Ministry of Defence.
The Board of Admiralty was created in 1628, when King Charles I put the office of Lord High Admiral into commission and transferred control of the Royal Navy to a governing committee.
The Admiralty was abolished as part of reforms that unified the Admiralty, the War Office, and the Air Ministry into a single Ministry of Defence. Its functions passed to a new Admiralty Board and Navy Board within that ministry.
The last person to hold the Lord High Admiral title as a working role was the future King William IV, in the early nineteenth century. After 1964 the title vested in the monarch.
The Admiralty Naval Staff was established in May 1917, replacing the earlier Admiralty War Staff. It handled senior command, operational planning, policy, and strategy for the British Admiralty until the department was abolished in 1964.
After 1964 the title of Lord High Admiral was vested in the monarch. Queen Elizabeth II awarded it to Prince Philip, Duke of Edinburgh on his 90th birthday in 2011, and it remained with him until his death in 2021.