A cyclist died while riding his bike along a popular countryside route near Hemel Hempstead on Saturday (September 5).
At around 3.30pm, a 46-year-old man was cycling along the Nicky Line, close to Redbourn Golf Course, when he fell from his bike.
Shortly after, the victim was then taken ill.
Paramedics were called to the scene but the man, from Harpenden, passed away shortly after.
Herts Police are now appealing for witnesses in a bid to try and piece together exactly what happened.
They say a boy was cycling with the man at the time of the incident.
PC Helen Carpenter, from the road crash investigation team, said: “We are hoping to piece together the circumstances of the incident that led to this man sadly passing away.
“A boy was with the man cycling on his bike at the time - did you see them cycling before the incident happened or did you see what happened for the man to fall from his bike?
“I’m appealing to members of the public who may have been in the area at the time and saw the incident take place, or the events leading up to it, to get in touch as soon as possible.”
Anyone with information is asked to contact police via the non-emergency number 101.