Larry Hagman’s addiction to alcohol, which at one time saw him down five bottles of champagne a day, was the likely catalyst for the medical problems that ended with his death Friday from throat cancer at age 81, a top doctor says.

The anti-rejection medications Hagman took following his 1995 liver transplant put him at high risk for cancer, said Dr. Chauncey Crandall, a specialist in cardiac transplantation at the world-renowned Palm Beach Cardiovascular Clinic in Palm Beach County, Fla.

Larry Hagman probably inherited a genetic tendency to cancer, but he was also such a severe alcoholic that he developed end-stage cirrhotic liver disease, which initiated a chain of events that hiked his cancer risk, Dr. Crandall said.

Hagman made J.R. Ewing on Dallas- one of TV’s most iconic characters. He was working on a new version of the show last October when he revealed that he had been diagnosed with throat cancer.

As J.R. I could get away with anything- bribery, blackmail, and adultery. But I got caught by cancer, Hagman said at the time. But he also vowed to beat it, saying, As we all know, you can’t keep J.R. down!

The announcement that he’d been diagnosed with throat cancer was not the first time that Hagman had faced the disease. In 1995, after a small tumor in his liver was discovered, he underwent a liver transplant, during which it was discovered that his liver had been so damaged by cirrhosis due to alcoholism that he nearly died after the 16-hour surgery.

In the heyday of Dallas, it got to the point where I showed up for work about 6:30 in the morning, and by around 9, I might have opened a bottle of champagne, which I would nurse until about noon, Hagman said in an interview. By lunch I might start on another half-bottle of champagne. I would go through about three bottles a day, sometimes with people who would drop by the set, but mostly by myself. I just kept that steady drip going. Often he would drink five bottles of champagne a day, Hagman admitted.

Although the liver transplant saved his life, the surgery also likely set the stage for throat cancer, Dr. Crandall said.

When Larry Hagman underwent his liver transplant, he had to take strong drugs that suppress the immune system so his body didn’t reject the new organ. Although this enabled him to survive the liver transplant, it also dampened his immune system, which is the body’s surveillance system that helps prevent cancer from developing, Dr. Crandall said. A study in the Journal of the American Medical Association last year found that organ transplant recipients have double the risk for cancer.

Even after his liver transplant, Hagman continued to drink, according to reports. We know that alcoholics are prone to throat cancer, said Dr. Crandall.

Hagman had other risk factors: He was a former smoker and his mother, the actress Mary Martin, died of colon cancer.

Larry Hagman had a genetic tendency for cancer, and yet he drank and he smoked, and he lived his life on the edge, said Dr. Crandall. He was a classic medical school textbook case for cancer risk factors because he had them all.

Read more: Larry Hagman’s Death: Alcoholism Led to Cancer