I want Queen, not King
Declassified: The 1987 files
William McCrea was angry that the Queen did not reply personally to a petition demanding a referendum on the Anglo-Irish Agreement.
After instead being sent a letter from Secretary of State Tom King, Mr McCrea sent it back.
The DUP MP wrote: "I wish to inform your boss that 'My Monarch is a Queen' and although the Secretary of State may be called 'King', he most certainly was not the person I petitioned."
The 1985 Agreement was the most important development in Anglo-Irish relations since 1920.
It granted the Republic a formal role in Northern Ireland for the first time since partition. But it sparked fury among unionists, who accused Margaret Thatcher's government of treachery.
In February 1987 unionist MPs delivered a 400,000-signature petition against the Agreement to Buckingham Palace.
It called for a referendum on the deal.
Officials who analysed the petition raised concerns about its authenticity.
A memo dated February 25, 1987 noted that some of the 404,074 signatures appeared to have been written by the same hand. Analysis of one sample found two incidents where six or more names had been signed by the same person.
However, they had no firm evidence of widespread fraud.