The Princess Royal attended a performance by the world’s oldest riding academy four months after suffering a concussion in a horse accident. Princess Anne watched eight riders and 26 horses from the Spanish Riding School in London perform synchronised routines on Friday evening. The academy, based in Vienna, Austria, has taught classical horsemanship in its Renaissance equestrian High School tradition for more than 450 years. The Princess was in attendance for the opening night of a tour by the school from the royal box on the opening night of the OVO Arena Wembley. She was joined by model Lad…