The 51-year-old was last seen leaving his home in the Welsh town of Talgarth to go for a run at 9am on Tuesday.
A team of about 50 people, including mountain rescue specialists, firefighters, and police spent four days searching for Mr Skeen on foot and using a drone.
Mr Skeen had recently moved to the Powys area from Bristol. Dyfed-Powys Police said the body has not yet been formally identified.
“But family [of Mr Skeen] have been made aware of the development,” a spokesman said on social media.
Former colleagues of Mr Skeen, who had worked for South Western Ambulance Service, had volunteered to help Longtown Mountain Rescue Team and Brecon Mountain Rescue Team search the Talgarth area on Saturday.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies