Hi Larry, you're right with Princess Mary. I know a story, that she shared time with Prince Charles, when he was a child. BTW, I read in a book, that Mary didn't attend the wedding of HM and Prince Philip because the Duke of Windsor wasn't invited - official version was, that she couldn't attend cause she was sick on this day.
I did a research today on the website of James Lascelles (Son of Earl Harewood and Greatgrandson of King George V.) and there's an interesting note - he is a musician - that he played last year in Highgrove with his band. It could be the 60th birthday of HRH, but I'm not sure.