William has in recent years taken up more official duties due to the queen’s age and ill health in a clear sign of his future role.
He called the queen, who died on Thursday aged 96, an “extraordinary leader”, praising her “absolute” commitment to Britain, the Commonwealth and the 14 other countries where she was also head of state.
“So much will be said in the days ahead about the meaning of her historic reign,” he added.
“I, however, have lost a grandmother. And while I grieve her loss, I also feel incredibly grateful.”
William – Charles’ elder son from his first marriage to the late Princess Diana – said he had benefited from the queen’s wisdom and reassurance throughout his life.
She had offered guidance and support to his wife, Catherine, while the couple’s three children – George, Charlotte and Louis – would have lifelong memories from the holidays they spent with her.
“She was by my side at my happiest moments. And she was by my side during the saddest days of my life,” said William.
“I knew this day would come, but it will be some time before the reality of life without Grannie will truly feel real.
“I thank her for the kindness she showed my family and me.
“And I thank her on behalf of my generation for providing an example of service and dignity in public life that was from a different age, but always relevant to us all.
“My grandmother famously said that grief was the price we pay for love.
“All of the sadness we will feel in the coming weeks will be testament to the love we felt for our extraordinary Queen.
“I will honour her memory by supporting my father, The King, in every way I can.”