Teen sensation Littler snatched second place in the World Darts Championship after an astonishing run.
He came away with a £200,000 runner-up prize – but will now lose at least 45% of it in taxes.
HMRC’s press office appeared to confirm reports about the huge tax take on Twitter.
It posted: “Big congrats to Luke on his fantastic run to the final.
“We can confirm the existence of income tax.”
Littler’s fans blasted the “brutal” Tweet from HMRC’s official press office account.
One said: “Sarcasm isn’t needed from the HMRC, thanks. It’s a terrible look for you.”
Another said: “Nothing funny about this Tweet. Inappropriate.”
A third said: “Quite an unpleasant, condescending response from HMRC, I feel – even though it may be technically accurate.”
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Investment platform Saxo said Littler will have to forfeit £76,203 of his winnings to the tax man – as well as £7,330 in national insurance.
Expert Andrew Mangion told Sky News: “Everybody needs to pay tax, no matter their age.
“Under 18s have the same personal allowance as adults.
“Normally children don’t work – or if they do, their pay is generally under the tax free allowance.
“In this case, it’s rare for a teenager to come into so much money in one lump sum.
“We would advise him to take professional financial advice on how to best act on this.”