Alison Krauss became Robert Plant's harmonies teacher.

The two artists release their second duets album, ‘Raise The Roof’ next week, 14 years after their first joint album 'Raising Sand’ was released to critical acclaim.

And the Led Zeppelin rocker has revealed he was too busy being a "rock 'n' roll cliche", to know about "strict melodies" and proper harmonising, and so he jumped at the chance to become a student when fiddle and harmony expert, Alison, coached him on how best to compliment her vocal.

Speaking to the new issue of Uncut magazine, Robert said: "As an English singer, I usually reach for the normal pop/rock stuff that I might have done with Zep on 'Thank You' or 'Little Drops Of Rain'.

"But Alison comes from a different world.

"She is always at pains to tell me that while was flying my kite in the back of a van she was seven years into fiddle competitions.

"She never went to prom because she was in the corner harmonising when I was already becoming a rock 'n' roll cliche at a very early age.

"She coaches me and gives me alternatives to bolster her vocal.

"She hears the way you can embellish a melody.

"I was learning all that Chitlin' Circuit phrasing in the mid-60s, so I never knew about strict melodies.

"I was very happy to put myself into the position of being a student to see if I could do it."

The 'Stairway to Heaven' hitmaker recently referred to their unique material as “dark and spacey”.

He said: “The wonderful thing about it is that it’s nameless, and it has its own personality. You could say it’s kind of a little bit retro-sounding. It’s almost an archival study of pretty far-out spacey music. I think you could call it dark and spacey.”