The story of an 8-year-old African boy who came to the U.S. with help from a retired NBA star for surgery to remove a large tumor from his face began as a heartwarming tale, but ended tragically.

Matadi Sela Petit, who was born in the Democratic Republic of Congo with a cleft lip and facial tumor that enlarged as he grew, died Friday at a Los Angeles hospital from a “rare and unpredictable genetic reaction to anesthesia," announced the foundation of former NBA star Dikembe Mutombo, which helped to sponsor his medical care.

“We are devastated by the loss of Matadi and our heart goes out to his father, his mother and the rest of his family, and all his old and new friends,” the Dikembe Mutombo Foundation said in a statement. "Despite the diligent efforts of his medical caregivers, Matadi did not recover and he passed away last night."

Matadi's trip to the U.S. and his surgery was also sponsored by several other partners, including the Ronald McDonald House and Cedars Sinai Hospital in Los Angeles.

He arrived in the U.S. with his father on Dec. 12 for the operation at the Osborne Head and Neck Foundation at Cedars Sinai. Mutombo met the pair at Los Angeles International Airport.

Mutombo said he got involved after meeting the boy and his parents this fall at a hospital his foundation built in his native Congo, according to TMZ Sports. The Biamba Marie Mutombo Hospital is named for the NBA star's mother.

"I was touched by what he's going through as a young boy who's 8 years old. Not going to school. The way he's been pushed away by the society," Mutombo said prior to the surgery. "His mom has to keep him in the bedroom every day because people are talking bad about him."

Matadi "was a pioneer, and his memory will inspire us to continue to develop efforts and partnerships to improve the lives of the children of the Democratic Republic of the Congo," the foundation said Saturday.

Founded in 1997, the Dikembe Mutombo Foundation aims to provide "high-quality health care to people regardless of their economic conditions," its website said.

Mutombo played 18 seasons in the NBA before retiring from the Houston Rockets in 2009. He holds the record for second-most blocks by an NBA player — 3,289, according to ESPN.com.