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By Erin Calabrese

Paul Kantner, one of the founding members of legendary rock group Jefferson Airplane, died Thursday surrounded by his family, his son told NBC News.

Kantner, 74, suffered a heart attack a couple of days ago, which led to multiple organ failure and septic shock, his son said.

"He passed today at 2:22 p.m. PT," Gareth Kantner said. "My brother, sister and stepmother were all present."

Paul Kantner performs on stage with the US rock band Jefferson Starship in 2009.PETER FOLEY / EPA, file

Cynthia Bowman, mother to one of Kantner's children and longtime publicist for all incarnations of Jefferson Airplane, said the outpouring of support has been overwhelming.

"I've received 112 calls in the past hour and that's just me," she said. "Paul was a very humble guy, he would be blown away by this ... It's unbelievable."

Kantner and singer Marty Balin formed Jefferson Airplane in the mid-1960s with musicians including Grace Slick and Jorma Kaukonen.

The band, known for classic tunes like "White Rabbit" and "Somebody to Love," was already set to receive a lifetime achievement award at the Grammy Awards in February. Jefferson Airplane was inducted into the Rock and Roll Hall of Fame in 1996.

Neil Portnow, president of the National Academy of Recording Arts and Sciences, called Kantner, "a key architect of in the development of what became known as the San Francisco Sound."

Reuters contributed.