A retired American man has hit the jackpot after he turned a measly $7 bet into nearly $1.5m - the day after his wife had officially beaten cancer.

Harold McDowell, 85, and his wife were gambling at the Borgata Hotel Casino in Atlantic City at the weekend when he decided to place a small bet down on a Six-Card Bonus in a game of Three Card Poker.

The dealer turned the cards over, revealing a straight flush of diamonds, - a hand dealt at 20 million-to-one odds.

After placing down the US$5 (about $7.43) bet, McDowell walked away with US$1 million ((about $1.49m).

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"I happened to be playing next to my wife. I had my back to her. I turned around said, 'I just won a million dollars,'" he told the New York Post.

"She told me, 'You're full of crap.' I was dumbfounded. I sat there like an idiot."

It appears the gods were looking down, smiling on McDowell and his wife after she was cleared of cancer just the day before the surprising million-dollar win.

McDowell explained his wife had liver and colon cancer for years, undergoing multiple surgeries.

"It was better news that she's healthy — money isn't the most important thing," he said.

McDowell plans to give most of the winnings to his children, saying his life will most likely stay the same but might treat his wife and himself to a cruise.