The singer/songwriter and longtime weed advocate makes the confession in his new memoir, It's A Long Story, which was released on Tuesday (05May15).

In the tome, Nelson recalls the 1977 incident, which happened after he spent a brief stint behind bars in the Bahamas for marijuana possession when then-President Jimmy Carter invited Nelson to the White House to thank the singer for his support.

Following a dinner with the U.S. leader, Nelson claims he was taken to the roof of the Washington, D.C. residence by a "White House insider" to see the city views at night.

Nelson alleges that the unnamed insider offered him a joint, and said, "Getting stoned on the roof of the White House, you can't help but turn inward... Certain philosophical questions come to mind, like... how the f**k did I get here?"

Nelson also writes about his passion for marijuana, calling it a loyal drug, which "has never betrayed me. Unlike booze, it had never made me nasty or violent. Unlike cocaine, it never sped me up or fired up my ego."

His love for pot initially landed him a stigma in the country music community, and even provided an awkward encounter with Spanish crooner Julio Iglesias when they recorded their hit To All the Girls I've Loved Before.

Nelson recalls he was advised not to smoke pot in front of former lawyer Iglesias, but the country star alleges that Iglesias wanted a "down-home atmosphere" in the studio and "lit up a fat one".