The envelope is the usual, with Prince Philip's badge on the back. You will notice that my address is printed on a sticker, that was then placed on the envelope. You will see this from time to time, mostly when envelopes are pre-stuffed with generic replies that can be sent to anyone who wrote for that occasion.
The envelope also features an accidental 2nd postmark, this time at the bottom of the letter. This postmark celebrates the Golden Man Booker Prize given to Michael Ondaatje's book The English Patient (published in 1992.) The Golden Man Booker Prize is a 1-time special award given to celebrate of the Man Booker Prize's 50th Anniversary. The Golden Man Booker Prize looked at every Man Booker Prize winner, over the award's 50-year history, to choose the best work of fiction.
The reply is the usual form letter from Prince Philip's office. The birthday message changes slightly from year to year. This year's message is identical to his birthday reply in 2015.
The letter reads:
Buckingham PalaceJuly, 2018
I have been asked by Prince Philip to say how much he appreciates your good wishes for his birthday.
Correspondence Secretary toH.R.H. The Duke of Edinburgh
What is interesting about this is it is signed by Suzy Lethbridge (signature printed on), Prince Philip's Correspondence Secretary. Previously every birthday reply I had received from Prince Philip had been sent by an Assistant Equerry. However, after Philip's retirement last summer, Prince Philip handed down his Assistant Equerry to his son, Prince Andrew.
The address, telephone number and fax are the general numbers for Buckingham Palace.