Frank Sinatra’s 1964 letter on son’s kidnapping that shows ‘rare vulnerability’ is up for auction

All eyes are on a never-before-seen side of “Ol’ Blue Eyes.”

A 1964 letter Frank Sinatra penned on the kidnapping of his son is being offered at Bonhams’ Unplugged & Unforgettable Music Auction, which starts Tuesday.

The six-page letter to a prison chaplain, regarding the infamous 1963 kidnapping of then-19-year-old Frank Jr., is estimated to fetch up to $30,000.

Frank Sinatra’s son Frank Sinatra Jr., was kidnapped in 1963. Arthur Pomerantz/celebrity.land Archives

Bonhams is auctioning a six-page letter that Frank Sinatra wrote about the kidnapping of his son. Courtesy of Bonhams

“The raw emotion portrayed in this letter reflects a man speaking openly, with less concern for the confines of public scrutiny. It’s this rare vulnerability that makes us especially excited to offer a glimpse into another side of a legend like Frank Sinatra,” Katie Allen, associate specialist for Bonhams pop culture in Los Angeles, told The Post.

In 1963, two amateur criminals, Barry Keenan and Joe Amsler, kidnapped Frank Jr., Sinatra’s son he had with his first wife, Nancy Barbato.

With the help of the FBI, the crooner paid a $240,000 ransom to have him returned safely.

Sinatra sent the note to Father Roger Schmit, the chaplain at the prison where Keenan was serving time, in response to the priest asking him to forgive his son’s kidnappers.

At the time, the kidnappers’ attorneys claimed Frank Jr. — a singer-songwriter who died in 2016 at 72 — staged his own kidnapping to gain fame.

“Their conduct in permitting this claim of ‘hoax’ was, in my opinion, another crime against society,” Sinatra wrote, adding that “the cloud of suspicion which hangs over [Frank Jr.’s] head will continue to affect adversely his life and his career.”

The lengthy letter could fetch as much as $30,000. Courtesy of Bonhams

The seller is the son of a man who was incarcerated in the same prison at which Schmit worked.

His father worked for Schmit and the chaplain gifted him the letter, which has been in his family since 1964.

Allen has her predictions on the type of “Chairman of the Board” fans who will bid on the letter.

“Memorabilia like this is perfect for a collector interested in who the man Sinatra was outside of the entertainment industry. It is a peek behind the curtain, so to speak, and opens itself to someone really trying to understand Sinatra as a family man.”