BLAKE SHELTON demanded justice when his good friend and mentor, country singer Wayne Mills, was brutally gunned down in a Nashville bar – and now he’s going to get it!

A Tennessee grand jury indicted the bar’s owner, Chris Ferrell, on second-degree murder charges for allegedly shooting Mills in cold blood during an altercation just days before Thanksgiving.

As THE ENQUIRER reported last week, Blake angrily vowed to use his fame and money to push for an exhaustive investigation into the slaying. And the “Voice” mentor is said to be satisfied that authorities have acted so swiftly.

“Blake feels totally vindicated,” said a close source. “He believed there was enough evidence to charge Ferrell with murder, and he’s glad the authorities agree with him.”

Ferrell surrendered to Nashville police on Dec. 6, and his bail was set at $300,000.

His defense attorney David Raybin declared: “My client denies that he’s guilty of any degree of homicide.”

But Blake is convinced that a jury will do the right thing and put Ferrell away for a long, long time.

Blake told a pal: “This guy cried that he shot Wayne in self-defense. Witnesses said that he shot him in the back of the head.

“He deserves to rot in jail for what he did!”

The 44-year-old front man for the Wayne Mills Band was killed in Ferrell’s Pit and Barrel bar after they got into an argument over Mills smoking in a nonsmoking area, say cops.

Tragically, Mills leaves behind his wife Carol, whom he met more than 20 years ago, and a 7-year-old son, Jack.

The loss left Blake inconsolable. Not only had he opened for Mills early in his career, he also considered him to be the man who put him on the path to country stardom.

“Blake felt he owed a great debt to Wayne,” disclosed the source.

And he was not alone in his love for the man friends considered a “gentle giant.” At a deeply moving Dec. 8 memorial service in Mills’ hometown of Arab, Ala., friends flocked to pay tribute to him, not only for his music but also for his generosity.

His friend Gary “Sarge” Sargeant, the head of Tennessee’s Outlaw Music Hall of Fame, recalled: “Wayne had a profound impact on everybody he met – the only thing bigger than his talent was his heart!”

He was also praised by his longtime pastor Don Ware who said: “When the tornadoes hit Arab (in April 2011), he was one of the first people to perform (to help raise money for disaster relief).”

Like Blake, Ware demanded justice, telling mourners: “We pray that…the perpetrator will reap what he has sowed.”

It now appears that justice will be swift for Ferrell, who was charged with domestic assault this summer. The assault charge was later dismissed.

Blake told a friend: “Nothing is going to bring Wayne back, but at least his family and friends can rest a little easier knowing that Ferrell is going to face a jury.”