Pop megastar Michael Jackson recorded a song written by a Bahraini prince planned as a charity single, a court ruling on a lawsuit between the two men has heard.

The unusual musical collaboration emerged as Sheikh Abdulla bin Hamad Al Khalifa, second son of the King of Bahrain, went to the High Court in London to sue cash-strapped Jackson for $US7 million ($A10.9 million).

The two men had a "close personal relationship," and even discussed the possibility of Jackson moving to Bahrain after his 2005 child sexual molestation trial, the sheikh's lawyer, Bankim Thanki, said.

"Sheikh Abdulla began to support Mr Jackson financially after 2005 when it became clear that Mr Jackson was in very serious financial difficulties, much to Sheikh Abdulla's surprise," Thanki told the court on Monday.

Assistants of Jackson initially asked the sheikh for $US35,000 ($A54,619) to pay utility bills at the pop star's Neverland ranch, followed by a request for $US1 million ($A1.56 million) dollars in April 2005, he said.

"Sheikh Abdulla made many more payments on his behalf or to others," including Jackson's $US2.2 million ($A3.43 million) legal bill for his criminal trial, he said.

The sheikh planned to revive Jackson's musical career, releasing records through their own label - including a song recorded the day after his trial ended, which the sheikh wanted released to help victims of the 2004 tsunami.

A recording of the song will be played in court during the trial.

"It shows the quality of Sheikh Abdulla's songwriting skills and that of Mr Jackson's voice," said Thanki.

The sheikh is suing Jackson for breaching a $US7 million ($A10.92 million) "pay-back" deal designed to repay money he advanced to Jackson when he was having his worst financial problems.

Jackson, who was not in court but has been called on to give evidence via video link from Los Angeles - contests the claim, saying the sheikh's case is based on "mistake, misrepresentation and undue influence".