The sports world has lost one of its stars. 

Former Denver Broncos running back Ronnie Hillman died on Dec. 21 following a battle with cancer, his family has confirmed. He was 31 years old. 

"It is with heavy hearts that we announce the passing of our beloved son, brother & father, Ronnie K Hillman Jr," the family wrote in a post shared to Hillman's official Instagram account. "Ronnie quietly and peacefully transitioned today in the company of his family and close friends. We as the family, appreciate the prayers and kind words that have already been expressed. We ask that you would give us time to process our feelings as we prepare to lay our precious RJ to rest."

In a separate statement hours before the former NFL player's passing, his family revealed that Hillman had been diagnosed with renal medullary carcinoma, "a rare but highly aggressive neoplasm form of cancer that primarily affects young African Americans with sickle cell trait," in August and that the treatment he'd received had been unsuccessful.