Lawford died of a heart attack Tuesday in Vancouver, Canada, his cousin, former U.S. Rep. Patrick J. Kennedy, told The Associated Press. He was 63.

Lawford’s mother was Patricia Kennedy, sister of John, Robert and Ted Kennedy, and his father was Peter Lawford, the English actor who was a member of Frank Sinatra’s “Rat Pack.”

“I was given wealth, power and fame when I drew my first breath,” Lawford wrote in his 2005 book, “Symptoms of Withdrawal: A Memoir of Snapshots and Redemption,” the first of several books he wrote about his substance struggles.

He spent his youth frolicking with Hollywood stars on one coast and rubbing shoulders with political stars on the other. He wrote that he once got a lesson in doing “The Twist” from Marilyn Monroe, and the cover of his books shows him sitting poolside as a child with his uncle and soon-to-be-president John F. Kennedy looming behind him.

Lawford leapt into drugs in 1970s Hollywood and struggled with addiction into the 1980s before spending his last decades in sobriety, and helping others — including his cousin — find their own.

“He was the absolute cornerstone to my sobriety, along with my wife,” Patrick Kennedy said Wednesday. “He was the one who walked me through all the difficult days of that early period.”

Lawford worked steadily as an actor but found only minor success. He had a small part in 2003’s “Terminator 3: Rise of the Machines,” made appearances on TV shows including “Frazier” and “The O.C.” and had recurring roles on the soaps “All My Children” and “General Hospital,” playing a senator in the latter.

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Dalton reported from Los Angeles.