The army lad, 22, and CBBC star Anna, 23, have been dating for almost two years.
Despite the alleged infidelity, friends claim the couple has overcome the betrayal and remains in a happy relationship.
The fling surfaced when George revealed the kiss on Chloe Burrows’ YouTube series and later reiterated the claim on his podcast.
A source added to MailOnline “This has been bubbling under the surface for months…
“But now Harry is on one of the BBC’s biggest shows so his relationship is in the spotlight.
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“Harry chose to forgive Anna, they’re all young and everyone makes mistakes.
“The cheating has become even more ironic because of his appearance on The Traitors, which is all about deception.”
The Sun has contacted reps for Harry for comment.
Harry has captivated viewers on the BBC series The Traitors, earning praise as the ‘greatest player ever’ for orchestrating a fellow Traitor’s elimination.