The Harry Potter actress, who played Hermione Granger in the film series, joked that her co-star - Draco Malfoy in the movies - 'broke her heart'.
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"Between the ages of ten and 12 I had a really terrible crush on Tom Felton, to the extent that I would go into work in the morning and look down the numbers on the call sheet to see if he was going to be in," Watson said on The Jonathan Ross Show.
"We love a bad guy, he was a few years older and he had a skateboard - and that just did it really.
"He totally knew and the thing is that he'd tell everyone, 'I see her in a younger, sisterly way', and it just broke my heart. It still does."
Watson added: "There was no romance between me and Daniel [Radcliffe] or Rupert [Grint]. The whole ten-year period I never so much as pecked one of them on the cheek."
The Jonathan Ross Show airs on ITV1 tonight (September 29) at 10.35pm.
Watch the trailer for Watson's new film The Perks of Being a Wallflower below:
