Martin Rixon, 29, hung on to hundreds of Japanese trading game cards, including Pokémon rarities, he collected when he was just eight years old.
After sitting forgotten in his bedroom in Barton-le-Clay for 20 years, his dad Neil recently decided to get them valued.
The evaluation left the pair stunned – with the collection tipped to net around £5,000 when it goes under the hammer at Hanson Ross Auctioneers.
Martin’s Pokémon hoard is expected to sell for between £2,000-£4,000 while his Yu-Gi-Oh! and Digimon cards are estimated to fetch £240-£460.
In addition, a collection of Mad Max toys, Top Trumps and Dragons could achieve £200-£400 in the sale in Royston, Herts., on November 17.
Amanda Butler, director of operations at Hanson Ross, said: “That promises to be quite a return for items bought for fun in childhood, the sort of stuff many people throw away thinking they’re simply not worth anything.
“Luckily Martin was wise enough to look after his cards and realised they could be valuable.
“It’s amazing to think something tucked way in a bedroom for 21 years can net that sort of return now.
“We were delighted when his dad brought the collection along to our Royston saleroom for valuation because Pokémon and rare vintage Japanese cards and gaming items are sought after at auction”.
Parents urged to check bedrooms for ‘forgotten treasures’
The director of operations at Hanson Ross continued: “It’s a burgeoning market sector that’s grown massively in recent years, fuelled by a global army of nostalgic fans”.
“Pokémon sparked a major card craze in the late 1990s and collections like this are probably gathering dust in many homes.
“If you have grown-up children in their 20s it might be worth checking their old bedrooms to make sure there aren’t any forgotten treasures from childhood tucked away in the wardrobe or under the bed.
“You never know, you just might be sitting on an auction windfall.”