Watch: Windsor Castle prepares for Prince Philip's funeral
Prince Philip admitted to waking up "in a cold sweat" after what he dubbed a "lame" toast to then-president Richard Nixon while at an event in the US, an unearthed letter has revealed.
Philip wrote to Nixon from Greenland in 1969, after travelling to the US on his own to carry out some visits across the country.
He had been hosted at the White House for a dinner when he made the diplomatic gaffe.
In a letter written to Nixon he said: "I can’t begin to tell you how much I appreciated your very great kindness and hospitality at the White House. I was quite overwhelmed by the guests but delighted to meet such a distinguished company.
"After the brilliance of the other speakers and yourself, I am afraid my contribution was very lame and that night I woke up in a cold sweat when I realised I had forgotten to propose your health! I do humbly apologise."
The letter has been dug out of the archives at the Nixon Presidential Library and shared with Yahoo UK.
While the letter is a matter of public record, it does not appear to have been reported on before.
During the trip to the US in 1969, Philip stayed with family friends in Wyoming and then was taken to the White House for a dinner in his honour.
After that he went onto New York, where he gave a TV interview to Barbara Walters.
The note continued: "The weather in New York was horrible but otherwise all went well and I found Miss Walters particularly charming and intelligent. I hope we did a good piece.
"Again with very many thanks for your great kindness."
The interview with Walters ended up becoming thought of as somewhat controversial as Philip offered a glimpse into the problems of Royal Family finances.
He said: "We go into the red next year, now, inevitably if nothing happens we shall have to - I don’t know, we may have to move into smaller premises…
"For instance, we had a small yacht which we had to sell, and I shall have to give up polo fairly soon…"
The comments were not well received in the UK, with the then-employment secretary Barbara Castle eported to have criticised the complaints from a man "married to one of the richest women in the world".
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And surprisingly, even though Prince Charles was only invested as the Prince of Wales in 1969, Prince Philip still had to bat away rumours about the Queen abdicating.
He told Walters: "As far as I know it's a rumour.
"It has its attractions. But no, I don't think it's been thought of very seriously. And in fact I'm not sure the advantages necessarily outweigh the disadvantages, so to speak, for this course.
"The idea that he would only be capable of making any contribution if he was sovereign is really not true. There have been so many cases where the heir has in fact had a very particular ability to do things that you wouldn't have otherwise. But who knows, it's all in the future, anything may happen."
Philip's 1969 US trip also included a brief stop in Iowa, which although was only to allow for refuelling resulted in the duke giving a short press conference and mingled with a crowd which had gathered to see him.
Richard Nixon was able to meet the Queen and Prince Philip on several occasions, starting in 1957 when he accompanied them as vice president during their US tour.
And in 1969 he was invited to Buckingham Palace and in 1970, he spent time with them at Chequers, which the official prime ministerial retreat.
Nixon died in 1994.
Prince Philip died on 9 April at the age of 99. A smaller, COVID compliant funeral will be held on 17 April for him at Windsor Castle.