In the last of three programmes, Andrew Marr looks at the defining moments of HM the Queen's reign, beginning with her accession to the throne in 1952 and her Coronation sixteen months later.He examines how she has coped with decades of changing and sometimes tense relations with the media, looks backwards and forwards at royal Jubilees and charts her trip to Australia to look at what some see as her most enduring achievement, the Commonwealth.And, for the first time, all of the Queen's adult grandchildren have their say about 'The Diamond Queen'.