A U.S. Border Patrol agent in Arizona died overnight, marking the second death of an agent while on duty this calendar year.

Robert Hotten, 44, is the second agent to have died on duty after Agent Donna Doss was fatally struck during a traffic stop in Central Texas in early February. Hundreds attended her funeral in Abilene, Texas, including the horse she rode as a Customs and Border Protection employee.

"Last night, we lost one of our own, U.S. Border Patrol Agent Robert Hotten. Agent Hotten was found unresponsive while on patrol in AZ. Agent Hotten, Class 910, served for 10 years in USBP. My thoughts and prayers are with his wife, son, loved ones, and colleagues," acting CBP Commissioner Mark Morgan announced in a Twitter post Monday afternoon.

Customs and Border Protection, the parent agency of the Border Patrol, has not specified how the agent died, and it is not yet clear whether foul play was involved.

Hotten had been on foot patrol in a "very remote mountainous area" when he was found, according to a CBP spokesman.

Fellow Border Patrol agents paid tribute via Facebook to Hotten, a Harley Davidson enthusiast who leaves a widow, Stacie, whom he married in 2010. "It always breaks my heart when I have to put this up," one posted. "But never as much as this time. My friend, colleague, and BP brother passed on duty last night. I’m missing you already brother."

Morgan emailed the 20,000 agents Monday morning informing them of the death, according to a copy of the email obtained by the Washington Examiner.

Hotten's death marks the 129th time an agent has died in the line of duty since Border Patrol was stood up in 1925.