The singer duetted with Minogue for the single “Kids”, which appeared on his 2000 album Sing When You’re Winning.
Williams has now revealed that, during their time working together, he fancied the Australian star.
During a new programme for BBC Sounds, titled Robbie Williams: My Life Thru a Lens, the former Take That band member was asked by Scott Mills: “You and Kylie – what was going on there?”
Williams, who has been married to Ayda Field since 2010, replied: “Not as much as I wanted it to be, unfortunately. Messed that up.”
The singer said he did this “just by 13 whenever I was around her”.
He added: “Like it’s the girl in the year above me, ‘I don’t know how to speak to you.’ My crush of all crushes.”
He previously said he has “the longest crush” on Minogue, telling British Vogue: “I was honoured and I still am to be on a record with her. Dreamy. Still crushed. Still crushing.”
Minogue has been in a relationship with the creative director of British GQ, Paul Solomons, since 2018.
Also during the interview, Williams opened up about his decision to leave Take That, calling the situation at the time a “burning building” from which he had to escape.