No mug's game: Earl Spencer in Wolverhampton to promote new book - WATCH
He had come to talk about history – but not this piece of history.
Earl Spencer was preparing to discuss his new book when given a drink in a mug chosen at random by a member of staff at Moseley Old Hall on the outskirts of Wolverhampton.
It had been made clear that he had no intention of engaging in conversation about his sister Princess Diana.
Then he looked at the mug and declared: "Oh look, it commemorates my sister's wedding."
There was a moment of stunned silence before he started laughing. He said later: "I thought it was a very charming touch by the people working here."
Moseley Old Hall features prominently in his book, called To Catch A King, which was why he was there to sign copies for people.
It concentrates on the six weeks the young Charles ll spent on the run before escaping to France after defeat at the Battle of Worcester, in 1651, two years after the beheading of his father Charles l.
Moseley Old Hall was one of the buildings were he was hidden while fleeing, with a vast price on his head, from the men who had the same beliefs as those who had killed his father.
Earl Spencer explained: "This is my fourth book on the Stuarts who I am particularly interested in because of the importance of the importance of the Civil War and the drama of that period.
"My last book was about the hunting down of the men responsible for the killing of Charles I and, to be brutally honest, one of the big Hollywood studios bought the rights to the book and they wanted more about Charles ll.
"It seems a bit like one of Cilla Black's Blind Dates, but then a man called Nigel from Lyme Regis, who had read the book, wrote to ask why it was so long since anyone did a book about Charles ll on the run.
"I discovered it had not been done since 1966 and the more I looked into it, the more fantastic I realised the story was. It is very dramatic.
"I also think that these days there is more of an appetite for history books that concentrate on a moment in time when everything hangs in the balance."
He said that Moseley Old Hall was central to the story. Soldiers twice called at the property while he hid there without finding the King.
Earl Spencer said: "There are other houses associated with his escape but this is the key one for me because it is where he was hidden by some of the most interesting characters. It gave him hope that he could escape the tens of thousands of people hunting him down."
Earl Spencer had visited the Hall as a visitor before returning to research the book and declared: "It is incredible to be in the house which, three and a half centuries ago, helped to save the King against almost impossible odds."
Charles ll was brought to Moseley Old Hall by Richard Pendrill and the first person in the queue on Suunday to get his copy of the book signed was Roger Pendrill, his 'great plus eight grandson.'
Mr Pendrill, aged 64, from Ackleton, Shropshire said: "It is so good that Earl Spencer has brought the story to life again."
Richard Pendrill was granted a £100-a-year pension in perpetuity for his help in saving the King. It is still paid to his family although Mr Pendrill is not among those to benefit from their £76-a-year share.
To Catch A King by Charles Spencer is published in hardback by William Collins, for 20.