Peter Philips has "always been very close" to Queen Elizabeth.
The 38-year-old royal - who is the son of Princess Anne and her first husband Captain Mark Phillips - is organising the Patron's Lunch to mark his grandmother's 90th birthday celebrations and feels "honoured" to have the chance to do so.
He shared: "I've always been very close to my grandmother, and we speak often. She has been an inspirational person throughout my life, so to be able to do something like this for her is an honour.
"As a child, I would attend charity events with my parents in school holidays, but as I've grown older the sheer number of causes of which the Queen is patron has become clear."
And Peter was keen to get his cousins, Princes William and Harry, onboard as he wanted to show the legacy the Queen has created during her reign.
He added: "One reason that I wanted my cousins, the Duke of Cambridge and Prince Harry, to be joint presidents of the Patron's Lunch is that very legacy. It is important that the Queen's charity work is not confined to a single generation. In the future the Princes will take on many of these patronages, just as the Queen inherited a great many of them from her mother, father and sister."
And Peter has praised the monarch for leading "by example" and completing her royal duties with "quiet diligence and astonishing humility".
Writing for The Telegraph newspaper, he explained: "From my early childhood - ever since I was causing havoc in the corridors of Windsor, Balmoral and Sandringham with my sister and cousins - it was impossible to ignore the standard my grandmother set when it came to her support of her patronages.
"For my whole family she has led by example, but never more so than in her dedication in this area. Over her reign, however, the Queen has gone about that work with quiet diligence and astonishing humility. So in this landmark year for her, I thought it high time her lifetime's unbroken service was acknowledged."