Top poker player Phil Ivey has lost a British Supreme Court challenge over his £7.7 million winnings from a London casino.
The 40-year-old American has been fighting to recover the money since successfully playing a version of baccarat known as Punto Banco at Crockfords Club in Mayfair in 2012.
Owner Genting Casinos UK said a technique he used called edge-sorting was not a legitimate strategy.
Mr Ivey maintained that he won fairly.
Today, five justices unanimously upheld the majority decision of the Court of Appeal, which dismissed his case on the basis that dishonesty was not a necessary element of "cheating".
Edge-sorting involves identifying small differences in the pattern on the reverse of playing cards and exploiting that information to increase the chances of winning.
Mr Ivey did not personally touch any cards, but persuaded the croupier to rotate the most valuable cards by intimating that he was superstitious.
In the Court of Appeal, Lady Justice Arden said the Gambling Act 2005 provided that someone may cheat "without dishonesty or intention to deceive: depending on the circumstances it may be enough that he simply interferes with the process of the game".
There was no doubt, she added, that the actions of Mr Ivey and another gambler, Cheung Yin Sun, interfered with the process by which Crockfords played Punto Banco with Mr Ivey.
That interference was of such a quality as to constitute cheating.
Mr Ivey argued that he did nothing more than exploit Crockfords' failures to take proper steps to protect itself against a player of his ability.
In the Supreme Court, Lord Hughes said it was an essential element of Punto Banco that the game was one of pure chance, with cards delivered entirely at random and unknowable by the punters or the house.
"What Mr Ivey did was to stage a carefully planned and executed sting."
He added: "If he had surreptitiously gained access to the shoe and re-arranged the cards physically himself, no-one would begin to doubt that he was cheating.
"He accomplished exactly the same result through the unwitting but directed actions of the croupier, tricking her into thinking that what she did was irrelevant."
Mr Ivey, said Lord Hughes, did much more than observe - he took "positive steps to fix the deck".
"That, in a game which depends on random delivery of unknown cards, is inevitably cheating.
"That it was clever and skilful, and must have involved remarkably sharp eyes, cannot alter that truth."
Mr Ivey said in a statement after the ruling: "It makes no sense that the UK Supreme Court has ruled against me, in my view, contrary to the facts and any possible logic involved in our industry."
He added: "At the time I played at Crockfords, I believed that edge-sorting was a legitimate Advantage Play technique and I believe that more passionately than ever today.
"As Mr Justice Mitting found, this is not just my personal view but one that 'commands considerable support from others' and I am grateful to the Supreme Court for confirming Mr Justice Mitting's finding that I was a truthful witness in this respect and that this was my honest belief.
"As a professional gambler, my integrity is everything to me.
"It is because of my sense of honour and respect for the manner in which gambling is undertaken by professional gamblers such as myself that I have pursued this claim for my unpaid winnings all the way to the Supreme Court.
"It is very frustrating that the UK judges have no experience or understanding of casinos and Advantage Play, or the ongoing battle between casinos and professional gamblers attempting to level the playing field.
"If they had, I am very confident the result in this case would have been in my favour."
Paul Willcock, president and chief operating officer of Genting UK, said: "We are delighted that the High Court, the Court of Appeal and now the Supreme Court have all found in Genting's favour, confirming that we acted fairly and properly at all times and that Mr Ivey's conduct did indeed amount to cheating.
"This entirely vindicates Genting's decision not to pay Mr Ivey, a decision that was not taken lightly."