Mixed martial arts fighter Allan Nascimento has died at the age of 34, according to a statement from the Ultimate Fighting Championship.

The UFC said Nascimento died on Monday after he was “found unresponsive after suffering an apparent heart attack in his sleep.”

“Despite the efforts of the responding medical team, he was pronounced deceased at the scene. Our thoughts and deepest condolences are with Allan’s family, friends, teammates, and loved ones during this incredibly difficult time,” the UFC added in its statement.

Nascimento, who was nicknamed “Puro Osso,” which translates to “All Bones,” was born in Brazil and held a 17-4 record in the country before taking part in Dana White’s Contender Series in 2018.

He signed with the UFC in October 2021 and made his UFC debut against Tagir Ulanbekov, where he lost in a split decision.

After losing to Ulanbekov, Nascimento achieved four consecutive victories against Jake Hadley, Carlos Hernandez, Jafel Filho and Cody Durden.

His final match was on June 20 at UFC Fight Night 279 against Mitch Raposo, who broke Nascimento’s winning streak via split decision.

Nascimento was scheduled to appear as a special guest at the Charles Oliveira Experience on Aug. 9.

The unexpected news of Nascimento’s death was met with shock around the UFC world.

Brazilian UFC fighter Caio Borralho wrote, “He was one of the most kind fighters that’s I’ve ever met! Polite, good energy and always in good spirits! He will be missed.”

“Today I lost a brother — a guy who was truly one of a kind — and the pain is unbearable,” Charles Oliveira said in a statement.

UFC correspondent Evelyn Rodrigues said Nascimento was one of “the kindest souls I’ve ever had the privilege of knowing through MMA. Rest in peace, Allan.”