Prince William admits the mourning process for his grandmother, Queen Elizabeth II, is making him relive the moment he walked in Princess Diana's funeral procession.
The Prince of Wales opened up Wednesday to folks outside Sandringham House ... they'd come to lay flowers there following the Queen's procession to Westminster Abbey, but ended up getting an interaction with William.
He told one woman who'd come to mourn the Queen that it's been difficult for the family to process the loss ... according to the Daily Telegraph. He said the ceremony brought back sad memories of his mother's death and funeral service.
Witnesses at Sandringham reportedly said the Prince's pain seemed evident in his eyes, and they claim he was close to tears.
As we reported, William and his brother, Prince Harry, walked behind their grandmother's coffin during Wednesday's ceremony as the procession went from Buckingham Palace to Westminster ... which is where QEII's will lie in State for a total of 4 days.
Her funeral and burial are set for Monday, Sept. 19.
You get why this all strikes a nerve for William and the royal family -- it was 25 years ago when Princess Diana was laid to rest after she was killed in a Paris car crash.