Caitlyn Jenner's ghostwriter William Hasley found dead on hiking trail

Caitlyn Jenner's friend and ghostwriter, William Hasley, has been found dead on Hollywood's famous Runyon Canyon trail.

According to the Los Angeles County Medical Examiner's office, Hasley died on Saturday 6 June at the popular hiking destination in Los Angeles. He was 78.

His cause of death has yet to be revealed.

The Los Angeles Fire Department confirmed to the New York Post that air rescuers had attempted to save the man but were unsuccessful.

"LAFD Air Operations lowered rescuers to the patient, and medical treatment was administered," an LAFD spokesperson told the publication. Officials pronounced Hasley dead at the scene.

Hasley started his Hollywood career in animation, writing for The Smurfs and Fat Albert and the Cosby Kids.

While working with NBC on the TV special Star Salute to the US Olympic Team, Hasley met Jenner, and the pair became good friends. In 1997, the Olympian commissioned Hasley to write the motivational book Finding the Champion Within, which was published under her former name, Bruce Jenner.

Hasley was previously married to The Bold and the Beautiful actor Robin Riker, who portrayed the role of Beth Henderson Logan on the long-running soap from March 2008 until the character's death in April 2010.