The story of Craig Sager's brave fight against leukemia has taken a heart-wrenching turn.

Less than a month after returning to work, Sager's leukemia has returned.

Craig Sager's son runs a 10k after donating bone marrow to his father

Probasketballtalk.nbcsports.com reported that Sager's son, Craig Sager II made the announcement on Twitter.

Sager returned to work March 5 at the Chicago Bulls game at the United Center against the Oklahoma City Thunder. The 63-year-old Sager, who was born in Batavia, Illinois, wore a red and black suit to commemorate his return to work in Chicago.

"I will come tonight, and you may actually think I'm Benny the Bull," Sager said at morning shootaround before that Bulls-Thunder game, according to probasketballtalk.com. "I have a lot of love for my Chicago Bulls. Normally, you don't show a lot of favoritism for one or the other team, but since Chicago means so much to me and coming back here, I said I have to show some love to the Bulls and to Chicago. I don't think I'll get booed by too many people for what I'm wearing here tonight."

It was such a touching occasion, with TNT capturing Sager's return. The snippet included Bulls coach Tim Thibodeau grinning from ear to ear during a pregame interview and welcoming Sager back to work.

Sager originally was diagnosed in April of 2014 with leukemia, just before the start of the NBA playoffs.

"I really thought I'd get back for baseball post-season, but that was far-fetched," he said, according to probasketballtalk.nbcsports.com. "I thought for sure I'd be back by [NBA season-opening] ring ceremony, and then I thought I'd be back by Christmas, or for All-Star. But it wasn't until Sunday that I took my final medication to keep my body from rejecting the transplant. Then I had to get the OK from the doctors from head to chest to feet, and they all cleared me with no restrictions. It all happened very quickly here at the end, but they said, "You're ready to go, and be careful." They still want me to wear a mask on the plane so I don't make the other people sick, but I guess I'm all right."

Let's hope Sager knows how to beat the disease and has a speedier recovery.