I don't care for the overly familiar use of nicknames myself (though I am guilty of the use of some for very common names) but Charley the Brat was a nickname that Charlotte used herself--signing it on several pictures. So while you might not like Eric's use of the nickname, it isn't one he made up himself to make Charlotte an object of ridicule.
The article does make reference to Charlotte: "They bear a "striking resemblance to their aunt, Princess Beatrice, and still more to their cousin, Princess Charlotte, eldest daughter of the German Crown Prince." Charlotte, who is married to the Hereditary Grand Duchess of Saxe-Meiningen, arrived in Darmstadt last night with her father, "to witness a ceremony in which she herself was not so very long ago the main actor.""