He made the comments in his role as a patron at the 25th anniversary gala of charity Child Bereavement UK and encouraged people to speak about their loss.
“For many, sharing their experiences and memories is a crucial part of the grieving process," the Duke said.
Following his visit to the National Memorial Arboretum to commemorate the 75th anniversary of the Normandy landings, the duke also spoke about the emotional impact on veterans.
He continued: “I saw that again in the eyes of D-Day veterans and families last week.
“Their sorrow for lost friends, sons and fathers 75 years on still moves them to tears.”
He praised the charity’s “great sympathy and sensitivity” in their work with “children, young people and families to help them navigate the difficult path of grief”.
William also met a number of people involved with the charity at the Kensington Palace event, including Mary Berry, who lost her teenage son in a car crash in 1989.
The celebrity baker and patron of the charity said: “When I lost my son there was no such thing as Child Bereavement UK.
“You don’t know where to turn, they really give such tremendous support.”