Rod Stewart's stepson Ashley Hamilton is threatening legal action against pop star Robbie Williams for allegedly stealing a track they collaborated on for his new album. Hamilton, the son of Stewart's first wife ALANA, is furious SHE'S Madonna appears on RUDEBOX without any mention of his input, and has vowed to drag his claim to rights through the courts if Williams doesn't compensate him. He insists the pair came up with the idea together three years (03), before Williams re-worked it with the Pet Shop Boys for his latest album. Hamilton fumes, "We came up with this idea over coffee one afternoon. "Robbie said he had an idea for a song about some girl he used to date, TANIA STRECKER, and how she was dumped by Guy Ritchie for MADONNA. "That was a slimey thing to do , so I said, 'Why don't we make a joke song about it?' We worked on the lyrics together at home and at the studio. "The next thing I know, a producer's ringing me up to say congratulations for getting my song on Robbie's record. I just said: 'I don't know what you're talking about!' "I was shocked. When you start working with someone, or you start an idea with someone, you're legally entitled to a share of the publishing. "I have the demos of that tape and will see him in court if I have to." Williams was found guilty of plagiarising another song in 2002 for his track JESUS IN A CAMPER VAN. He was ordered to remove it from hit album I'VE BEEN EXPECTING YOU and pay out substantial royalties.