Prince. Picture: Supplied

Prince's infamous vault of unreleased music was literally kept in a vault inside his Paisley Park home, complete with heavy metal vault door.

The 'Purple Rain' hitmaker tragically passed away in 2016 from an accidental fentanyl overdose at the age of 57, leaving behind a vast collection of unreleased music which was known only as "the vault".

And it has now been revealed that this collection - which was named so after the room typically found in a bank which keeps valuables secure - was literally kept behind a hefty metal vault door in his Paisley Park home, which was found within another room clearly labelled "The Vault".

According to The Blast - which obtained police photographs of the room which were taken two weeks after the star passed in April 2016 - the room included several framed photos of the 'Little Red Corvette' singer, alongside his copious awards and gold records.

Within the outer "Vault" room was an actual metal door which led to another room filled with recordings, whilst the room next door housed guitars and drum kits.

The obtained pictures come after authorities in Minnesota - where Paisley Park was located - announced on Thursday that no criminal charges would be filed in relation to the iconic musician's passing.

Carver County attorney Mark Metz said in a statement: "Despite the intensive law enforcement investigation, there is no reliable evidence showing how Prince obtained the counterfeit Vicodin laced with fentanyl, or who else may have had a role in delivering the counterfeit Vicodin to Prince.

"Therefore, without probable cause and no identified suspect, the Carver County Attorney's Office cannot file any criminal charges involving the death of Prince.

"There is no doubt that the actions of individuals around Prince will be criticised, questioned and judged in the days and weeks to come. But suspicions and innuendo are categorically insufficient to support any criminal charges." 

Recently, to mark the second anniversary of the icon's passing this month, his estate ventured into the vault to release a never-heard-before original recording of 'Nothing Compares 2 U', which Prince gave to his side project, The Family, six years before Sinead O'Connor put her spin on it in 1990.