The Duke of Cambridge has paid tribute to the Queen describing her as a "wonderful great-grandmother" for his children and very much his "boss".
Speaking at a early birthday party for the Queen, who turns 90 next week, William described her as a "guiding force" for her family.
The Duke's words honouring the monarch were spoken at the special event staged in New Delhi as the second day of his and Kate's tour of India and Bhutan came to an end.
Earlier the couple visited the site where India's founding father Mahatma Gandhi was assassinated, to honour his memory.
In a poignant ceremony they scattered rose petals where the man who led India to independence was shot and killed in 1948.
And they also commemorated India's First World War dead by laying a wreath at India Gate, the nation's war memorial, despite strong gusts that threatened to lift up the Duchess' dress.
At the birthday party William, watched by wife Kate who wore a monochrome outfit by Alice Temperley, and dozens of guests, said: "I am incredibly lucky to have my grandmother in my life. As she turns 90, she is a remarkably energetic and dedicated guiding force for her family.
"And I am so glad that my children are having the chance to get to know the Queen. George and Charlotte, too, will discover how lucky they are to have such a wonderful great-grandmother - a role model for the rest of their lives.
"Now, it is important that everyone here tonight understands that I am here as the Queen's representative. She may be my grandmother, but she is also very much the boss."
The Duke told the guests, gathered at the British High Commission, that the Queen was very fond of India and had visited three times during her 64-year reign.
He added: "And India of course is the biggest country in the Commonwealth, the family of nations to which she has committed so much of her life's work. India's contribution to the Commonwealth is something that is enormously important to her."
The Duke read out a message from his grandmother in which the Queen said she was delighted the Cambridges had been able to join the guests.
She added: "I have fond memories of our previous visits to India. This event today is a wonderful opportunity to celebrate the enduring friendship between our two countries, our shared culture and the business opportunities we can create together.
"It is with great pleasure that I entrust another generation of my family to strengthen and renew our bonds."
At the end William joked: "Now I can report back to Granny that I have done my duty."