Humperdinck, born plain Arnold George Dorsey in Leicester, began his fling with South African actress Juliet Prowse, once Sinatra’s fiancee, in 1967, after he had become friends with the Rat Pack.
The singer had been invited to appear on Dean Martin’s hit US television show after his song Please Release Me had become a huge hit in Britain.
‘After the show Dean invited us to his restaurant. Dean was there with his agent Mort Viner and Frank Sinatra, who was with his girlfriend Juliet Prowse, and Jilly Rizzo. Engelbert and I were both terrified. Going to a fancy restaurant was a big deal for us in those days.
‘What made it worse was that during the meal I noticed that Juliet was staring at Engelbert. I could see she fancied him. I took him aside and whispered, “Whatever you do remember that’s Sinatra bird.” I thought that would put him off.’
Over dinner, Martin invited Humperdinck to open for him in Vegas. At the Riviera Hotel, Dean’s name was up in lights, but not Engelbert’s – because it was too long. ‘I went absolutely potty but there was nothing they could do,’ said Cartwright.
‘Out of the blue one day I got a phone call from Jilly Rizzo who summoned me to his suite at Caesar’s Palace." said Cartwright. ‘His tone of voice was icy. He told me that he knew about their affair, that it was a big problem, and that I had to end it immediately.
‘I raced back to the Riviera where Engelbert and Juliet were together, and banged on their door. I told them what had happened and Eng was as terrified as I was, although Juliet was more cool. I got her out the back of the hotel and the affair ended there and then. And luckily Sinatra never found out.