LORD Mountbatten – who was assassinated by the IRA – privately wished for a united Ireland, according to the files.
The Queen’s cousin told the Irish Ambassador to London in 1972 that he would be happy to help with efforts to secure a lasting peace on the island.
Just seven years later, he was blown up, along with two teenage boys, while on board his boat off the small fishing village of Mullaghmore, Co Sligo.
The IRA said it carried out the murders to highlight the continued British presence in Northern Ireland.
But Mountbatten was hopeful that political developments in the early 1970s would lead to reunification, according to papers just released into the National Archives in Dublin.
The then Irish Ambassador to London, Donal O’Sullivan, told his Department of Foreign Affairs about his meeting with the Earl at a banquet given by the Queen at Windsor Castle on April 11, 1972.
Paraphrasing their conversation, he said Mountbatten hoped that Prime Minister Edward Heath’s approach to the North would secure reunification.
“Lord Mountbatten said he wished me to know that he and many of his friends have been deeply impressed by the positive Dublin reaction to the Heath initiative,” Mr O’Sullivan wrote.
“They hope that this can be developed into a ‘major advance towards the final solution’. Reunification is the only eventual solution.
“If there is anything he can do to help he will be most happy to co-operate.”
Mountbatten was also the Duke of Edinburgh’s uncle as well as a close friend and mentor to his great nephew, the Prince of Wales.
Mr O’Sullivan painted a picture, through regular dispatches to Dublin in the early ’70s, of a broad desire among senior figures in the British establishment for eventual reunification.
In one report from a meeting with Mr Heath on August 1, 1972, he wrote: “He then talked freely about reunification, which he is confident must come about.
“The British Government will put no obstacle in the way of reunification once the will for it exists.”