Prince William surprised Princess Diana’s supporters with a touching gesture this week.

On Monday night, the Duke of Cambridge made a surprise appearance outside Kensington Palace to meet with well-wishers who held a vigil to mark Princess Diana’s birthday on July 1.

Prince William told those who were gathered outside the palace that he’s grateful to them because they always remember his late mother on his special day. After just seven minutes, the dad of three stepped back into his home because the crowds started piling up outside the gates.

No one knew that Prince William would personally thank Princess Diana’s supporters on Monday night. In fact, it seems that the Duke of Cambridge didn’t also plan on meeting his mom’s fans. This is because Prince William was accompanied by just a small team of security.

During official and announced royal engagements, members of the British clan are accompanied by a massive group of security.

One royal fan shared details about his encounter with Prince William and said that the royal shook his hand along with five others who were also there.

“William told me he knew we’d been coming here for years and thanked us for what we were doing for his mother. I’m still shaking now, I feel very emotional,” John Loughrey told Daily Mail.

Meanwhile, Princess Diana would have been 58 years old if only she were still alive. The Princess of Wales passed away on Aug. 31, 1997, following a fatal car crash in Paris.

At that time, Prince William was just a teenager and Prince Harry was only 11 years old. Following Princess Diana’s shocking demise, Prince Charles flew to Paris to recover his late ex-wife’s body.

Prince William and Prince Harry joined Prince Charles and Prince Philip in walking behind their mom’s casket during her funeral. Princess Diana’s younger brother, Charles, Earl Spencer also walked behind his older sister.

Prince William
Prince William attends the unveiling of The Victoria Cross Commemorative Paving Stones representing each of Birmingham's 1st World War recepients at the Hall of Memory, Centenary Square on Dec. 7, 2015 in Birmingham, England. Getty Images/Richard Stonehouse