The wrestler did add, though, his doctors are "very optimistic that they caught it early."

Duggan had battled the disease for most of 2021 ... needing multiple procedures -- including one in which doctors removed his prostate -- to try to eradicate it. In December, he said medical experts had declared him officially cancer-free.

But, the 68-year-old said in a video message on Sunday that it had returned ... adding, "It's a very terrifying time for me and my family."

Duggan said he's now gearing up to undergo more treatments to try to get rid of the disease ... explaining in his video message he's set to have radiation therapy for eight weeks, five days a week.

"Hacksaw" said doctors are optimistic about the potential results of the treatments, and added they're encouraging him to "go ahead and live life."

"Which we're going to go ahead and do," he said.

"I'm afraid I'm going to make most shows, but some shows, I'm going to have to postpone or cancel," Duggan added. "And, I'm sorry about that, but that's the way it's got to be."

In addition to his 2021 battle with cancer, Duggan also battled the disease in his 40s -- and has dealt with heart problems as well. He did say that fans' support has helped him through it all -- and he's hoping for a similar outcome this year.

"You folks have helped me through an awful, awful lot over the years, many times before," he said. "And, sharing this with you is going to help me get through this. So, thank you."