BBC News
By Owen Amos
image captionPrince Philip at Sandringham for the Christmas service in 2017
It was a cold morning on the Sunday between Christmas and New Year, and Cat Kidd was among the well-wishers at Sandringham in Norfolk, waiting for the Royal Family to arrive at church.
Cat, now 34 and living in Cambridge, is from the area, and would often visit Sandringham with her family to see the royals traditional Christmas church visit.
On this morning, five or six years ago, Prince Philip spotted Cat in the crowd. To her surprise, he said something. So what was his festive greeting?