There is no accepted code of behaviour for encounters with royalty, but adhering to the traditional forms of address will prevent anxiety. When meeting any member of the Royal Family, men should bow from the neck, and women should make a small curtsey. A handshake is also acceptable. For male members of the Royal Family, use ‘Your Royal Highness’ and subsequently ‘Sir’. A female member of the Royal Family – except The Queen – should be addressed as ‘Your Royal Highness’ followed by ‘Ma’am’.
Should you happen upon a member of the Royal Family during their time off, allow them the freedom to go about their business as an ordinary person. Assume that to royalty, being left alone is far from a discourtesy; it is a luxury.