Stevie Wonder and Chaka Khan perform at Prince tribute concert

Stevie Wonder and Chaka Khan have paid tribute to Prince at a four-hour memorial concert in Minnesota.

The show began with a short video message from President Obama, who said: "Thank you, Prince, for all the great works you have done.

"You will be in our hearts forever."

Singer Morris Day, one of Prince's childhood friends, later took to the stage with his band The Time, playing hits such as Jungle Love - which Prince wrote for the band under a pseudonym.

Khan brought Wonder on stage to duet on I Feel for You, a track from Prince's debut album, which Khan covered in 1984.

Wonder recreated the harmonica solo he had played on that single, before the duo performed 1999 - one of the night's highlights.

Other performers on the bill included Tori Kelly and Prince's backing bands The NPG and 3rd Eye Girl.

X Factor judge Nicole Scherzinger joined the latter for a cover of Nasty Girl, a hit single for Prince protegees Vanity 6 in 1982.

She said it was an "honour" to celebrate the star.

Singer Christina Aguilera pulled out of the show at the last minute, citing a "vocal illness" - despite fans hearing her rehearse I Wanna Be Your Lover during the day.

She was replaced by British star Jessie J, who performed Nothing Compares 2 U.

John Mayer, who would have recreated some of Prince's pyrotechnic guitar solos, also pulled out, as the concert apparently clashed with recording obligations with his band. Soul star Anita Baker was a no-show due to injury.

That left a lot of the heavy lifting to Prince's lesser-known protegees and associates. Former backing singer Marva King got the crowd on their feet for Kiss, while singer-songwriter Judith Hill performed a playful piano rendition of How Come You Don't Call Me Anymore.

Hill, who recorded an album with Prince last year, also turned in one of the night's more sombre moments, playing the religious ballad The Cross, from Sign O The Times, which features the lyric: "Don't die without knowing the cross".

"I know that Prince is alive and well and he is happy right now," Hill told the 18,000-strong audience at the XCel Energy Arena in Minnesota's capital Saint Paul.

Prince's ex-wife, choreographer Mayte Garcia, recreated an segment of the star's 1993 Act I tour, in which she performed an elegant belly-dance with a sword balanced on her head, before segueing into the song 7.

The show concluded after midnight, with Stevie Wonder playing an extended version of his funk classic Superstition, after he giving a heartfelt speech about how he would "miss Prince forever".

Purple confetti fell from the ceiling as the band played Purple Rain, accompanied by Prince's pre-recorded vocals.

The star's younger sister, Tyka Nelson, described the concert as a public memorial for Prince fans.

"I want them to get some closure," she said. "It takes time to kind of get over it, and I see that they are grief-stricken."

She said there would "definitely" be future concerts.

Remembered for such hits as Purple Rain, Raspberry Beret and Alphabet Street, Prince blended elements of jazz, funk, R&B, disco and rock in a prolific career that produced more than 30 albums.

Video testimonials said the star anonymously spent a great deal of his fortune on charity, despite his image as a recluse.

Van Jones, a former adviser to President Obama, said fans would be stunned to know the number of projects secretly funded by the musician, who had turned to him for logistical help.

"I don't think Prince wanted to save the world. I think what Prince wanted to do is make sure that people's gifts... had a chance to sing," he said in a video.

The singer died of an overdose of the painkiller fentanyl in April, leaving a vast trove of unreleased music, but no will.

Courts in the US are trying to decide how to divide up his estate, with several potential heirs coming forward in the months after his death.

It was reported on Thursday that his "vault" of unreleased recordings was being shopped around record labels with a price tag of up to $35m.

However, Londell L McMillan, Prince's longtime lawyer, manager and friend, who was appointed to oversee his estate, has denied the story - which originally appeared in Billboard magazine, and was reported by the BBC, amongst others.

"Please don't believe that absurd article on the vault," he wrote on Twitter. "There are so many false rumours."

The BBC contacted McMillan for further comment, but he has yet to respond.

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