Since her death in December, some unlikely friends of Carrie Fisher's have emerged.

James Blunt, for example, has spoken movingly about the late actress - who was godmother to his child - and now Sean Lennon has shared a song that he co-wrote with Fisher before her death.

Lennon, who called her "one of the best and closest friends I’ve ever had in my life" uploaded the demo of 'Bird Song' to Soundcloud, explaining that it was written years ago but only recorded after she passed away.

"Carrie and I wrote this song years ago,”he said. “When she died I just felt I had to record it. This is only a demo unmixed, we only had a few hours to record it. But the lyrics she wrote with me I think are marvelous."

The female vocals, meanwhile, are provided by none other than Willow Smith.

Hear it below: