London (CNN)The Duke of Cambridge has paid tribute to Queen Elizabeth II on her 90th birthday for helping him cope with the loss of his mother, Diana, Princess of Wales.
"She's been a very strong female influence," Prince William said on Sky News. "And having lost my mother at a young age, it's been particularly important to me that I've had somebody like the Queen to look up to and who's been there and who has understood some of the more, um, complex issues when you lose a loved one."READ: Queen Elizabeth's guide to globetrottinghttp://edition.cnn.com/2016/04/20/travel/queen-elizabeth-travel/index.html
How is the Queen celebrating?
Last year, the Queen gained the title of Britain's longest-ever reigning monarch. On Thursday, she achieved another milestone as the nation's first sovereign to celebrate her 90th birthday.
She plans to mark the day with a walkabout near her main residence in Windsor, west of London, before lighting a beacon relay in the evening.
Later in the summer, formal celebrations will be held to mark her "official birthday," culminating with a national service of Thanksgiving at St. Paul's Cathedral and a giant picnic outside Buckingham Palace for 10,000 guests.
On Wednesday, the monarch's celebrations began with another first: an official photograph of four generations of royals, featuring three future kings posing at Buckingham Palace. The image of the Queen, and Princes Charles, William and George will be on special stamps issued to mark the Queen's life.
It's a milestone for 2-year-old Prince George, who makes his "stamp" debut, his first of many to come, pictured standing on a stack of blocks for a boost.
In contrast to the 64 years of service carried out by his grandmother, Prince William answered criticism in a separate interview of his commitment to royal duties -- he's been called "Workshy William" by some UK media -- saying he is willing to take on more responsibility when the time comes.
"I take duty very seriously. I take my responsibilities very seriously," he told the BBC. "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."