Prince William has said he will honour the memory of his grandmother, Queen Elizabeth, by working to support his father King Charles.
"My grandmother famously said that grief was the price we pay for love," he said in a statement.
"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."
Charles, 73, was officially proclaimed Britain's new monarch in a ceremony earlier on Saturday, having immediately succeeded his mother when the 96-year-old Queen died on Thursday.
William, 40, who is now the heir to the throne, said that the Queen "was by my side at my happiest moments. And she was by my side during the saddest days of my life".
"I knew this day would come but it will be some time before the reality of life without Grannie will truly feel real."
On Friday, Charles on Friday bestowed on William the title Prince of Wales, which he previously held.
William's wife Kate was given the title Princess of Wales, which was previously held by Charles' late first wife, Diana.