Stephen Mulhern, 32, who hosts the 'extra' hightlights ITV2 spin-off show, reckons the pair have also had a quick smooch.
While posing for a group hug, music mogul Simon, 49, took things to the next level and planted a jokey one on Amanda.
'When we were filming the last show before the live finals start, Amanda and Simon had a bit of a snog,' he tells The Sun.
'I was stunned I'd say it went on for about three seconds. Piers Morgan was a bit left out.'
Amanda, 38, is married to record producer Chris Hughes.
The scenes will air on Britain's Got More Talent on 23 May.
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