Dan Hill was rummaging through a box of costume jewellery when he found the sparkler.
Although Dan, who presents Dave's Storage Hunters UK, has no expertise in jewellery, he decided to pay the £1.50 the woman asked for it.
And he was right to, because when he had it valued later, he was told it was white gold diamond ring worth between £4,500 and £5,000.
This wasn't the first time the furniture dealer had had luck at this particular car boot sale either - he once bought hundreds of oil paintings for about £100 and then sold the 60-70 big ones for between £100 and £150 each.
Dan now plans to sell the ring, although his wife Louise quite fancied keeping it.
He was quoted in the Sunday Mirror, saying: "I always buy things from a gut feeling. I'm not an expert in jewellery but it looked quality.
"I've had a lot of success at car boots but this is definitely the best thing I've bought for £1.50. I feel pretty proud of myself."
We bet he does!
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