The former band mates have been fighting over royalties for years
A copyright dispute over Procol Harum's hit A Whiter Shade Of Pale has been heard by the Law Lords.
Matthew Fisher, who played the organ on the track, claims he is entitled to a share of royalties dating back to 1967.
In 2006, the High Court ruled he was entitled to 40% the copyright, but that decision was overturned by London's Court of Appeal last year.
Lawyers say it is the first time the Law Lords have been asked to rule on a copyright dispute involving a song.
The hearing is expected to last two days. The judgement will be reserved and given at a later date.
Mr Fisher claims he wrote the haunting organ melody which forms the basis of Whiter Shade Of Pale - recently named the most played tune in British public places over the past 70 years.
He began legal proceedings at the High Court three years ago, but eventually lost because the Court Of Appeal said he had waited too long - 38 years - to bring his case.
Lord Justice Mummery said in his ruling last April that Mr Fisher, now a computer programmer from Croydon, south London, was "guilty of excessive and inexcusable delay in asserting his claim".
"He silently stood by and acquiesced in the defendant's commercial exploitation of the work for 38 years," he added.
As a result, the copyright reverted back to Procol Harum frontman Gary Brooker and lyricist Keith Reid.
In this week's hearing, the Law Lords will set wide-ranging guidelines for how long a person can wait before bringing a case to court.
Mr Fisher's Counsel, Iain Purvis QC, stood before the panel of five Law Lords to present his case.
"We say for all practical purposes the appeal court confiscated his [Mr Fisher's] share of the copyright and awarded it to the defendants," he said.
He explained that Mr Fisher was taking legal action to be recognised as the joint author and owner of one of the "most famous and popular works of the 20th century, and that he has achieved".
"But secondly, to receive the income to which he says he is entitled as the co-owner of the musical copyright."
Mr Brooker's solicitor, Lawrence Abramson, has said that if the law Lords overturn the Court of Appeal's ruling, the implications for the music industry could be severe.
He said it would open up the prospect of countless claims from musicians who felt their contribution to a song had been overlooked in some way, regardless of past contracts.