And if that wasn't incredible enough, they then found out they lived just one mile apart.
When they were 14 years old, schoolgirls Sue Ellis and Yvette Metay, from Paris, became good friends and Yvette often visited Sue in Staffordshire.
Sadly, their years of letter writing came to an end in 1973 and they lost touch.
Yvette then moved to the UK when she finished her studies in 1976 and married Steve Pearson - a friend of Sue's ex-boyfriend.
Sue had no idea her French friend was living in England, even though she had introduced her to Steve on one of her visits from Paris.
Then in a bizarre coincidence, both of the women eventually ended moving to the Staffordshire town of Hednesford – and now live just one mile apart.
However, they had no idea they were living so close to each other until they bumped into each other for the first time in 40 years at Aldi last August.
They are now best friends, meeting up twice a week for coffee, and were guest of honour at each others 60th birthday party.
Recalling their reunion, Sue, who lives with her partner Steve Price, 59, said: "I was standing at the checkout and I saw a woman in front of me and just knew I'd seen her somewhere before.
"I just couldn't place her but suddenly she spoke and I recognised her slight French accent.
"It's really funny to hear Yvette speak now as she still says some phrases in a really Midlands accent.
"We were chatting for ages blocking the entrance and then we saw each other a few days later and I went around her house which was less than a mile from mine.
"We now see each other every week and met up in time for her to come to my 60th party in September and I went to hers in January.
Yvette, who works as a French teacher, added: "Sue came over to me as she'd seen me come out of the shop on her way in and watched me for a while to make sure it was me.
"She just said my name and I couldn't place her but knew that I knew her.
"I started looking down her face and then she smiled and I knew straight away that it was Sue.
"I knew the second that I saw that smile. It was fantastic.
"Through my whole career I've told the kids I teach that if they get the chance to have a penfriend they should take it because you never know where it will lead."
More on Parentdish: Pen pals around the world
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