Ukrainian President Volodymyr Zelenskyy on Saturday paid tribute to three Ukrainian pilots killed in a mid-air collision, including one with the callsign “Juice” who gained prominence for giving anonymous media interviews during Russia’s war in the country.

“Yesterday, a catastrophe in the sky over the Zhytomyr region killed three pilots, including Andriy Pilschikov, callsign ‘Juice,’” Zelenskyy wrote on X, the platform previously known as Twitter. “My heart goes out to the pilots’ friends and loved ones. The investigation is ongoing, and the truth will be revealed.”

Pilschikov was killed during a combat mission when two L-39 planes collided, the Ukrainian Air Force said on X. He was not piloting the planes, but was there in an observing capacity, according to a U.S. official.