Britain's Prince William has opened up about the "grief" he experienced when his mother died.

Prince William

Prince William

The 33-year-old royal paid a touching tribute to his late mother, Princess Diana, during an emotional speech at a gala celebrating the 21st anniversary of the Child Bereavement Charity, of which is mother was a dedicated supporter.

He said: "Twenty-one years ago last month, my mother attended the launch of the Child Bereavement Charity. Fifteen years later, I was honoured to be invited to become Patron of Child Bereavement UK to continue my mother's commitment to a charity which is very dear to me.

"What my mother recognised back then ­and what I understand now is that grief is the most painful experience that any child or parent can endure."

Prince William and his brother Prince Harry were just 15 and 12 years old, respectively, when Diana was killed in a car crash in 1997.

The Duke of Cambridge - who now has children Prince George and Princess Charlotte with his wife Duchess Catherine - continued: "I have witnessed first-hand the difference CBUK has made­ and continues to make ­to the lives of bereaved families. CBUK works with military families, with the wrecked families of suicide victims, with little children whose lives are torn apart by the inexplicable death of a parent. And yet amid all this misery, CBUK ­- and I don't know how they do this ­- brings warmth, comfort, a guiding hand, a way through, even colour and joyfulness, and a renewed opportunity for love as a family reknits itself after tragedy."

William opened up about this mother's death for the first time last year after being made patron of the organisation.