By Gemma Strong Prince Louis was desperate to get his hands on a crown of his own, after spotting his big sister Princess Charlotte receiving one as a gift. It’s been revealed that Princess Kate took her two youngest children to Elstree Studios last December for a secret visit behind the scenes of the hit BBC TV show Strictly Come Dancing. Head judge Shirley Ballas later spoke about the royal outing and shared a sweet anecdote about little Louis and Charlotte. “They are beautiful. When they visited we had these crowns on set, so I thought it would be a nice idea to give the little girl a crown…