At the age of 82, Willie Nelson is in a class of musician all his own. However, when the still touring musician postponed a few shows scheduled with Merle Haggard fans across the world were a little worried.

In an interview with the Washington Post Nelson revealed the reason for the surgery and show cancellations.

It was a stem-cell operation. It’s supposed to help the lungs. Over the years I’ve smoked a lotof cigarettes, and I’ve had emphysema and pneumonia four or five times, so my lungs were really screwed up, and I had heard that this stem-cell operation would be good for them. So I said, “Well, I’m gonna try it out.” But I’m still so sore that I can’t say that it was a success. I’ll have to wait until all the soreness goes away.

Check out the full interview here.