COURAGEOUS actor Michael York has been secretly battling a rare, killer blood disorder and friends fear he’s nearing the end.

“We’re afraid Michael’s dying,” says a longtime pal. “We all knew by his appearance there was something serious going on, but he didn’t talk about it.

“Michael always seemed boyish. But these last couple of years he appears to have become an old man who’s in constant pain.”

The 71-year-old British actor is suffering from amyloidosis, a debilitating and possibly lethal blood disorder that deposits abnormal proteins throughout the body and breaks down tissue.

York, who starred as D’Artagnan in the 1973 hit “The Three Musketeers”, underwent an unusual stem-cell transplant at the famed Mayo Clinic in Rochester, Minn., followed by chemotherapy treatments that made his hair fall out.

But he says he believes he’s beating the disease.

“They said it would be six months before the tissue even starts to heal, and I’m sort of in that ballpark now and am noticing an enormous return of energy,” he says.

“I lost my voice – completely. Now it’s sort of back.I know this can be deadly, but I never gave up. I am thrilled at this reprieve and want to do as much as I can to make it better.”

York first realized his health was in danger two years ago when “I noticed I was getting dark circles under my eyes. At first, I was able to cover them up with makeup, but it got worse and I had to wear dark glasses.”

York’s fans feared something was terribly wrong when his face was bruised, puffy and yellowish at the 2012 TCM Classic Film Festival in Hollywood last April. In January, his voice was hoarse and his face was still swollen and pale at a Cabaret reunion with former co-stars Liza Minnelli and Joel Grey in New York.

York says “the meds” he’s taking and “the illness” have left him bloated. But the star, who’s been wed to photographer Pat McCallum for 45 years, says he’s hoping for a full recovery.