In case you didn't know, Judas Priest's Rob Halford and Lady Gaga have been friends for years.

Now, Halford has revealed how the two became friends and which Judas Priest and Lady Gaga songs he would love to perform with the Artpop star.

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Halford first found out that Gaga was a Judas Priest fan when he saw a photo of her wearing one of the band's shirts. For Halford, he shares that he has always big a big fan of Gaga.

″[I] instantly knew she was going to be gigantic as an artist,″ Halford says. ″I became a big fan of everything that she's done and that's because I love all kinds of music. She's the best at what she does.″

Then, Halford and Gaga finally met in 2014 through their mutual friend DJ Lady Starlight. Starlight invited the Judas Priest vocalist to a Gaga concert. During the performance, he quickly learned that Gaga is actually a fan of Judas Priest.

″When Gaga started her performance, me and Starlight snuck out into the audience,″ he says. ″I was clapping and hooting and hollering like fans, and Gaga's making her way out to them and then she sees us, and she literally falls to her knees and crumbles onto the floor."

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As Starlight predicted, Gaga was very happy that Halford had shown up to watch her performance.

″And Starlight's digging me in the ribs going, 'See, I knew she'd be happy that you were here,'″ he says. ″She's so pure, she's so in touch with herself as a person, and the great, great, great, great things that she's done for the LGBTQ community.″

Following this fateful day, the duo became instant friends. Now, Halford has revealed which songs he would love to perform with Gaga someday.

″I would definitely do 'Born This Way' because that's our anthem,″ he says in reference to the LGBTQ+ community. ″As far as Priest songs go, I think I'd like to do 'Breaking the Law' with her because it talks about the frustration that we go through, particularly as young people. You don't know what it's like, you haven't got a clue. You'd do the same thing too, breaking the law."

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Halford details his friendship with Gaga and other experiences in his new autobiography Confess. In the book, he reveals that he knew he was gay since he was 10. However, this discovery was during a time when gay men were "full-on persecuted" in the U.K. Eventually, when he was 13, he came out to his parents who were supportive.

″God made me this way,″ he says. ″This was placed inside of me. This is who I am.″

Confess is out now and you can purchase your copy here.

Did you know Lady Gaga and Rob Halford were friends? Are you going to read his new autobiography? Let us know in the comments below.