Prince Louis has once again caused mischief while on a royal outing as he blew out his sister Princess Charlotte’s candle during his mother’s carol concert. Princess Charlotte, Prince Louis and Prince George watched their mother, the Princess of Wales, host the special festive service at Westminster Abbey last night. The three posted letters to other children before The ‘Together At Christmas’ Carol Service at Westminster Abbey. After the service, Prince Louis blew out Charlotte’s candle as their mother Kate laughed. He was pictured puffing his cheeks in an attempt to extinguish his older sist…