Frank Sinatra Jr, who followed in his famous father's footsteps to forge a career in music, has died of a heart attack while on tour in the US.

In a statement, his sister Nancy said: "The Sinatra family mourn the untimely passing of their son, brother, father, uncle Frank Sinatra Jr of cardiac arrest while on tour in Dayton, Florida."

The 72-year-old had travelled there to perform his Sinatra Sings Sinatra show, where he does renditions of his father's greatest hits.

Sinatra Jr was famously kidnapped at gunpoint as a teenager, by young men who were demanding a ransom of $240,000 (£168,000).

Two days later, he was released unharmed after the money was paid - and the criminals behind the kidnap plot were later jailed.

In the years before his father's death in 1998, Sinatra Jr served as the iconic singer's musical director and conductor.

He was Sinatra Sr's middle child, and in interviews, described seeing the likes of Dean Martin and Sammy Davies Jr perform from the wings of the stage.

In a recent interview with The Daytona Beach News-Journal, he said he never felt ashamed for failing to achieve the dizzying fame enjoyed by his father.

He said: "I think in my generation, when I came along in the early 1960s, the type of music that was in vogue in society in those days had moved on to another type of music.

"I was trying to sell antiques in a modern appliance store."

Sinatra Jr is survived by his son, Michael.

(Sky News)