Thirty-four-year-old Nigel Brookes was given the valuable cards by his mother back in 1999 when he stopped other kids conning his then-seven year old brother out of his best cards.
As a reward - and even though he doesn't even like Pokémon - his mam gifted him a full set in a presentation case.
Pokémon fan or not, he's glad she did now, because he's been sitting on a rare collector's item for 21 years, and it's significantly increased in value.
Nigel, who has three children of his own now, said: "Jeremy [his younger brother] ran into the house showing off this new Pokémon card he had traded with the kids on the street.
"I knew straight away that what these kids had done is told Jeremy their cards were better and traded them with him for his cards, which were really rare.
"My brother was really sad about it and when our mum found out, being the big brother, she wanted me to sort it out.
"I found the kids and got my brother's card back, so as a present, my mum brought me this rare collection direct from the Pokémon creators in the US for about £300."
"I wasn't actually that interested in Pokémon.
He continued: "I was disappointed at the time because the collection was one of my birthday presents so to me it was waste of a present.
"Little did I know they would be worth £35,000 now, we have kept them in the family for over 20 years and now they're going up for sale for a collector who will take care of them.
"There are 103 cards in total, they are all in pristine condition and were bought direct from creators 'Wizards Of The Coast' in the US, and are all first edition.
"My daughter Layla loves Pokémon and did try to buy them all of me for £6 - unfortunately that won't cut it, and I'm sure she'll appreciate why I said no in the future!"
The cards are set to go under the hammer on 27 July, and they are expected to attract attention from all around the world.
Auctioneer Richard Winterton, who will wield the hammer at Lichfield Auction Centre, said: "The collection is estimated to fetch in the region of at least £25,000 and £35,000 and is viewed as something of a Holy Grail for serious Pokémon aficionados all over the world."
Nigel concluded: "It was a difficult decision to part ways because I'm sure in 20 years they'll be worth double.
"My kids are growing up and I want to be able to give them a really special childhood. With this money we can really set ourselves up for the future."
"It is also scary having this collection. If there was a flood, they got damaged, lost, or ruined in some way, they wouldn't be worth anything.
"Now I think it's time to get our money's worth and enjoy ourselves."