Tom Petty and the Heartbreakers is coming out with a special box set featuring four CDs of previously unreleased music. 

The upcoming four-disc compilation is titled American Treasure and it is set to arrive on Sept. 28. The news was announced by SiriusXM's Tom Petty Radio on Tuesday, July 10.  

Tom Petty's 'American Treasure'

The box set, according to Variety, was collated with the help of Petty's widow Dana York, their daughter Adria Petty, his Heartbreakers bandmates Mike Campbell and Benmont Tench, and frequent collaborator Ryan Ulyate, a music producer and sound engineer. 

A total of 60 songs will be included in the upcoming box set, some of which were unreleased live and studio materials while others were alternate versions from the singer-songwriter's long and successful career. 

On Tuesday, SiriusXM played a sample of one of the tracks that will be included in American Treasure. The radio station previewed the unreleased song called "Keep A Little Soul" which was recorded in 1982. 

In addition, the box set will feature an artwork by Shepard Fairey. 

American Treasure is the first release of the Rock and Roll Hall of Famer following his death in October. A less expensive, two-disc collection is also expected to be released. Fans can expect more details to be released by Wednesday when the timer on Petty's official website reaches zero. 

Tom Petty's Overdose

Petty was one prolific singer-songwriter. Along with the Heartbreakers, he released 13 albums since they launched in the 70s. He also released three solo albums including Hypnotic Eye, the final album he released under his own name. He also contributed to Mudcrutch alongside members of his pre-Heartbreakers bandmates. 

In October, the beloved music icon was found unconscious inside his home in Malibu. He was temporarily put on life support, but he died hours later. 

He was 66 years old. 

In January, a toxicology report revealed that Petty passed away due to an accidental overdose. The attending examiner-coroner said that the world-renowned musician had traces of drugs, acetyl fentanyl, and despropionyl fentanyl in his system.

On a statement posted on Facebook, his wife and daughter disclosed to fans that Petty suffered a number of ailments in his final months. They said that his condition worsened because he continued touring with the Heartbreakers until September. 

"We knew before the report was shared with us that he was prescribed various pain medications for a multitude of issues including Fentanyl patches and we feel confident that this was, as the coroner found, an unfortunate accident," the statement read

Petty was laid to rest in a quiet ceremony attended by family and close friends last fall.