“Sleep Well, Your Majesty”

King George V, Queen Mary and Princess Elizabeth with their Cairn terrier named Snip, 1928. Image from the Royal Family's Twitter page. 

Little Princess Elizabeth has a great liking for her grandfather, his Majesty the King; which he returns; but, however much he might indulge her, she never forgets to treat him with the respect due to his rank. When the time comes to say good night, with all the courtesy of an old time courtier, she retreats backwards to the door and before it closes, curtseys and says:

"I trust your Majesty will sleep well."

 Source: Browse  Western Mail, Thu 19 April 1928 , Page 17