Diana’s family joined the two brothers for the ceremony at the palace’s Sunken Garden, a place in which the princess once found solace.
It was the first time the brothers have appeared in public together since the funeral of their grandfather, Prince Philip.
The brothers later issued a joint statement in which they described their mother’s strength and character as “qualities that made her a force for good around the world.”
“Every day, we wish she were still with us, and our hope is that this statue will be seen forever as a symbol of her life and her legacy,” they said.
The statue is the creation of sculptor Ian Rank-Broadley.