His death was announced by his family members, who revealed that his cause of death was a cardiac arrest he suffered during a tour in Daytona Beach, Fla., on Wednesday.
Sinatra Jr., like his famous father, was a Jersey boy, born in Jersey City, N.J., in 1944. He was returned safely after two days when his family paid 240,000 dollars for his release.
The son of the legendary singer died unexpectedly from a heart attack while on tour in Florida.
Sinatra Jr. followed in his father's footsteps and began performing in clubs as a teen.
Francis Wayne Sinatra, known professionally as Frank Sinatra Jr.
Talking about his own career, he said: "I've never been a success".
National Football League rule changes include chop block, extra points, horse collar tackles
Next, the chop block rule in which one player blocks and opponent high while another chops at his legs, is now considered illegal. That rule is now permanent, and the line of scrimmage for PATs will remain at the 15-yard line going forward.
Sunday's concert was the first time Mr. Elko, of Elko Concerts, worked with Mr. Sinatra, who he said hadn't toured in more than a decade.
The similarities were clearly evident on Sinatra Jr.'s 1996 Sinatra tribute album, As I Remember It.
Keenan masterminded the kidnapping, prosecutors said.
He wrote: "I always admired Frank Sinatra Jr. I got to get up with big orchestras and sing my father's music and it's a gift".
In this file photo, singer Frank Sinatra Jr performs at the 15th annual Society of Singers ELLA Awards in Beverly Hills, California in this September 12, 2006, file photo. Thoughts with his mother Nancy, sisters Nancy and Tina and his son Michael.
Nancy Sinatra Sr., sits beside a piano with her young children, Nancy Sinatra, Frank Sinatra Jr. and Tina Sinatra circa 1960s. However, he was declared to have been legally insane when he kidnapped Sinatra Jr. and his sentence was reduced as a result and in 1968 he was paroled after having served just four-and-a-half-years in prison. His manager Andrea Kauffman made the announcement, which led to an outpouring of condolences and support from friends and loved ones.