On screen, Phil Leotardo and Tony Soprano were foes; the heads of the New York and New Jersey crime families respectively on the hit HBO series “The Sopranos.” Off screen, Frank Vincent and James Gandolfini comprised a cast that for the past 24 hours, has consistently described itself as a big family.

“Probably one of the finest actors I’ve ever worked with; a very professional guy,” Vincent said via telephone about his on-screen enemy, following the news that Gandolfini died in Italy at the age of 51. “He never let his talent get in the way of his friendship. He was a sweetheart of a man and it’s very tragic that this happened.”

Reports Tuesday night suggested that Gandolfini may have passed away from a heart attack. An autopsy has yet to be performed. Vincent said he did not know of any health issues with the star.

“Jimmy was always a big, healthy, hearty guy,” he said. “Who knows? 51 years old… they say when you’re young and you get a heart attack, it’s not the best thing in the world. It’s a shock to everybody.”

Vincent filmed for years with Gandolfini, and looks back fondly on the times they spent together.

“All the stuff in the Bada Bing that we did and all the stuff in the houses… I mean, it’s just a sad thing. I feel bad for his family.”