Lottery bosses are investigating claims a thief stole a winning £600,000 ticket.
The ticket was bought by a man in Crawley on October 24 for the following day's game.
He was ecstatic when all his numbers came up and put the winning ticket on the dining room table at his home. The next day the ticket was missing.
Several weeks later the 70-year-old, who is originally from Cyprus, said a young man approached him in his driveway.
The man, who was in his early 30s and tall, slim and well-spoken, said he had stolen the pensioner's ticket and cashed it.
He had spent some on a seafront property in Brighton and a car but his conscience had prompted him to return the rest.
The younger man drove off before giving more details, leaving no contact number.
The victim, who asked to remain anonymous, said: "Every morning I wake up and my stomach is turning at the thought of my stupidity.
"I had left the patio door open and I believe that's how he must have got into my house.
"I don't care about the money for myself but I've been doing the lottery for years to help my two children. I know this man has a conscience because he came to see me before. I would appeal to him to come back and return the rest of the money."
A spokeswoman for Camelot said anyone who suspected they had a lost or stolen ticket should contact the company's prize payout department in Watford.
For more information, call 0845 9100000.
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