NEWS EDITORIAL USE ONLY. NO COMMERCIAL USE (including any use in merchandising, advertising or any other non-editorial use including, for example, calendars, books and supplements). This photograph is provided to you strictly on condition that you will make no charge for the supply, release or publication of it and that these conditions and restrictions will apply (and that you will pass these on) to any organisation to whom you supply it.  All other requests for use should be directed to the Press Office at Kensington Palace in writing.    This undated photo has been released by the Duke and Duchess of Cambridge of Prince George, who celebrates his fourth birthday on Saturday. The picture was taken at Kensington Palace in London at the end of June by Chris Jackson, Getty Images Royal Photographer. (Photo by Chris Jackson/Getty Images)