Robert Plant and his band the Sensational Space Shifters were joined by Pretenders frontwoman Chrissie Hynde during their performance at London’s Royal Albert Hall. You can watch the guest spot from on Friday, which features performances of  “Bluebirds Over the Mountain” and the Pretenders’ “2000 Miles,” above.

Plant’s cover of Ersel Kichey’s “Bluebirds Over the Mountain” appears on his latest album Carry Fire; Hynde also performs on the studio version. They've known each other for “35 years, 40 years, just en passant,” the Led Zeppelin icon told TeamRock. “I like the sweetness of the song. It’s cute, and it’s a song I used to sing when I was a kid, before I was a singer. It’s a sort of nursery rhyme.”

It also represents a rare look back for the ever-restless Plant. "Each time I feel the incentive to create new work, I must mix old with new," he said in an album-announcing statement. "Consequently, the whole impetus of the band has moved on its axis somewhat – the new sound and different space giving way to exciting and dramatic landscapes of mood, melody and instrumentation.”

Time has given him a sense of perspective, rather than a dollop of nostalgia. “I’m no longer a teenager, but I’m aware as time goes on, if you listen to singing about love, it’s usually broken love," Plant said. "It’s seldom you extoll the virtues of a life in successful love. Show me a happy writer, I’ll show you a rubbish writer! I see things going on around me; I see the rub of love, the energies, the electricity. I’m not giving up – I have a season ticket.”