Dikembe Mutombo Sorrowful Over Loss of Child with Tumor But Vows to Keep Helping

Dikembe Mutombo's heartbroken over the loss of Matadi Sela Petit, but incredibly ... he's staying positive, and says the tragedy's only strengthened his focus on helping people.

The Basketball Hall of Famer tells TMZ ... he's been working with the 8-year-old boy's family to transport his body back to the Democratic Republic of Congo for a proper burial, which should happen soon. He says dealing with the loss is tough ... but everyone's hanging in there.

We broke the story ... Dikembe flew the child from Africa to the U.S. earlier this month in hopes of removing the large tumor from his face, so he could return to his home and live a normal, happy life.

Matadi and his family stayed at the Ronald McDonald House in L.A. as they awaited his operation, led by Dr. Ryan Osborne from Cedars Sinai Medical Center ... who volunteered his services.

Sadly, Matadi suffered a rare genetic reaction to anesthesia during his surgery last week and went into cardiac arrest, and despite the best efforts of the medical staff ... he passed away Friday night.

Dikembe's remaining devoted despite the sad outcome, though -- reminding us things don't always turn out the way we want ... and are sometimes out of our control.

Mutombo also says there are no plans to change anything at his hospital in the Congo -- which has helped hundred of thousands of people -- and he vows to keep the good work up.

As we reported, Dikembe's foundation says 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."

He was 8.