Top poker player Phil Ivey has lost a 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.
On Wednesday, 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.