(FoxNews) – Sean Kiernan may get as much as $4 million for a piece of 
Hollywood history that his father, Bob, acquired for just $3,500 and
refused to sell to Steve McQueen, the actor who drove it in the 1968
action film "Bullitt."

When the classic-car insurer Hagerty sent car expert Kevin Marti to
authenticate the vehicle, he couldn’t believe his eyes, according to a 
New York Times report: “Ninety-eight percent of the original car is
there,” Marti told Hagerty. “It’s an incredible artifact.”

Since ‘Bullitt’s’ release, the 1968 Highland Green Mustang has become
one of the best-known vehicles shown on the big screen. McQueen
himself even tracked down Bob Kiernan in 1977 and wrote him a letter
asking to buy the muscle car back, according to the Times.

“I would like very much to keep it in the family, in its original condition
as it was used in the film, rather than have it restored, which is simply
personal with me," McQueen wrote in the missive detailed by the Times
which reported that Bob Kiernan never wrote McQueen back.

Sean Kiernan of Nashville stands next to the Ford Mustang GT 390
driven by Steve McQueen in the cult classic film "Bullitt."

Steve McQueen, starring in the title role of "Bullitt," steps out of his
car after a pursuit through the hilly streets of San Francisco.