The 18-minute track was penned by frontman Bruce Dickinson and will feature on their 16th record The Book Of Souls. Their first-ever double album will be released worldwide on September 4.

Harris tells Kerrang: "I think it's a masterpiece, actually - I think I can say that because I didn't write it! It sounds like Maiden but it's totally different from what we've done before.

"Eighteen minutes sounds like a long time, but it's actually such a journey that� well, it's best just to leave people to listen to it and see what they think. But it's very interesting. It's certainly not boring."