LONDON, ENGLAND - MAY 15:  HRH Prince Harry (L) joins former service men Andy Phillips (C) and Daniel Whittingham (R) in a live Twitter Q&A session at the top of the BT Tower to answer questions about the Invictus Games following the launch of the tickets going on sale on May 15, 2014 in London, England.  (Photo by Tristan Fewings - WPA Pool /Getty Images for Invictus Games)