The Secret Service agent assigned to protect Jacqueline Kennedy Onassis is writing a book about his experiences traveling across the world with the late former first lady, People magazine reports.

Clint Hill, who guarded Onassis as part of his 17-year-long career in the Secret Service, will publish My Travels With Mrs. Kennedy with Gallery Books this fall. The book, which will feature more than 200 “rare and never-before-published photographs,” is co-written with journalist Lisa McCubbin Hill, Hill’s wife.

The publisher says the book will “reveal never-before-told stories of…Hill’s travels with Jacqueline Kennedy through Europe, Asia, and South America.”

Hill was assigned to Onassis’ detail after the 1960 presidential election. He is well known as the Secret Service agent who jumped onto John F. Kennedy’s limousine after the president was assassinated in Dallas.

He said he was spurred to write the book after rediscovering a collection of letters and photographs related to his travels with Onassis.

“When you travel with someone, you experience things that can’t fully be appreciated by anyone who wasn’t there,” he said.

Hill and McCubbin Hill are the authors of three previous memoirs: Mrs. Kennedy and Me, Five Days in November, and Five Presidents: My Extraordinary Journey with Eisenhower, Kennedy, Johnson, Nixon, and Ford.

My Travels With Mrs. Kennedy is scheduled for publication on Oct. 11.

Michael Schaub is a Texas-based journalist and regular contributor to NPR.