Queen's 90th birthday :- Prince William pays tribute

Prince William has answered criticism of his commitment to royal duties, saying he is willing to take on more responsibility when the time comes. He was speaking in a BBC interview in which he paid tribute to the Queen on the eve of her 90th birthday. She had been a "guiding example" of what a good monarch should be, he said. Meanwhile, a picture of the Queen, the Prince of Wales, Prince William and Prince George, for stamps to mark the monarch's birthday, has been released. Prince William told BBC royal correspondent Nicholas Witchell: "I think the Queen's duty and her service, her tolerance, her commitment to others - I think that's all been incredibly important to me and it's been a real guiding example of just what a good monarch could be. "And it's been incredibly insightful for me growing up, watching her leadership in that role. "I think it's important to grow into a role with the right characteristics and the right qualities, and I think she's exemplified that in everything she's done." The prince's own commitment to royal duty has been questioned in some quarters in recent months - there have been headlines in some newspapers which have referred to him as "workshy William". He said he did not ignore such criticisms but did not take them completely to heart. "I take duty very seriously. I take my responsibilities very seriously. But it's about finding your own way at the right time and if you're not careful duty can sort of weigh you down an awful lot at a very early age and I think you've got to develop into the duty role," he said. William emphasised the importance he attached to his role as an air ambulance pilot and to the time he spent with his family. He said both his father and grandmother fully supported the fact that he was not yet fully engaged with royal duties, but that when the time came to accept more responsibilities he would be the first person to put up his hand and take them on. Queen's 90th: What's happening and when? *20 April - The Queen will visit the Royal Mail delivery office and open a bandstand, in Windsor *21 April - She will unveil a plaque on Windsor's Queen's Walkway, before lighting the first of a chain of beacons. Gun salutes will also be held across the UK *12-15 May - Celebrations featuring hundreds of horses and performers in the grounds of Windsor Castle *10 June - A national service of thanksgiving at St Paul's Cathedral *11 June - The annual Trooping the Colour at Horse Guards Parade *12 June - The Queen will host a street party for 10,000 people in the Mall Ten special stamps have been released to celebrate the Queen's birthday, including a stamp sheet featuring four generations of the Royal Family. The picture of the Queen, Prince Charles, Prince William and Prince George was taken in Buckingham Palace last year. George, making his first appearance on a Royal Mail stamp, had to stand on four foam blocks bound together with tape so his head was at roughly the same height as the seated royals. Six further stamps have been released for the head of state's 90th birthday, three focusing on the Queen's family life and three honouring her official role. On Wednesday, the Queen, accompanied by the Duke of Edinburgh, will meet staff and view an exhibition at Windsor's Royal Mail delivery office. Her visit marks the 500th anniversary of the postal service and she will hear the Royal Mail choir sing. The royals will then head to Alexandra Gardens in the town for a ceremony to officially open a new bandstand and meet pupils from the six schools involved in its decoration. On her actual birthday on Thursday, the Queen and Prince Philip will undertake a walkabout in Windsor and unveil a plaque marking The Queen's Walkway, a 6.3km self-guided walking trail connecting 63 points of significance in Windsor. It was designed to recognise the moment the monarch broke the record on 9 September 2015 held by her great-great-grandmother Queen Victoria by being on the throne for