A rare throwback photo of Princess Diana with her two sons, Prince William and Prince Harry, has just been released.

The picture is included in “Escorting the Monarch: We Lead, Others Follow” by Chris Jagger. In the snap, Princess Diana is watching over her two sons as they ride the Special Escort Group’s (SEG) motorbike. Young Princes William and Harry even had helmets on.

Jagger’s book examines the history of the SEG, a unit of the Metropolitan Police Force responsible for escorting high-profile families and individuals around London. It is also the job of the SEG to ensure the safety of the person or people they are watching over.

The author of the book revealed why he decided to publish a story centered on the SEG. He said that he grew up on fun stories about the SEG because his dad was a retired SEG himself.

“Many provided incredible insights to a world that was otherwise closed off. As a teen, I had the privilege of spending a day here and there to watch the SEG at work – a visit to a secret office or a royal palace was often on the cards. For a young north London lad, this was very inspiring to say the least,” he said.

Jagger added that majority of people know the SEGs. However, not everyone is aware of the stories regarding their services. He also said that the royal family developed a close relationship with the SEG because the latter accompanies the former almost everywhere.