The former Take That star, 48, teamed up with Minogue for the song Kids back in 2000.
But Williams – who has been married to his wife Ayda Field for 12 years – said he “messed up” his shot as he didn’t know what to say to the Locomotion star, reported The Sun.
The chart-topper spilled the beans on BBC Radio 2's Robbie Williams: My Life Thru A Lens when he was asked whether there had been anything between him and the Neighbours actor back then.
"Not as much as I wanted to be unfortunately,” Williams was quoted as saying.
"I messed that up by being 13 whenever I was around her.
"It was like the girl from the year above me - 'I don't know how to speak to you!'"
"But she's my crush, my crush of all crushes," added the star.
The Let Me Entertain You singer went on to meet and fall for Ayda and they tied the knot in 2010.
They welcomed daughter Teddy in 2012 and son Charlie followed two years later.
In 2018 they had daughter Coco via a surrogate and in 2020 they revealed that they had used the same surrogate to have a baby boy named Beau.
Minogue, who is now 54, is in a relationship with Paul Solomons, the creative director of British GQ magazine and GQ Style magazine. The pair have been dating since 2018.
Watch: Ayda Field details her and Robbie Williams' sex life