"We started to draw it in a drawing book my mum had given me, but most of it was actually done by John.
"She kept it until about 10 years ago when she gave me the book, but I didn't look at it. It was only when I sorted through it recently that I discovered it. I couldn't believe it."
The whales were washed up in the River Mersey in September 1953 and the one Lennon based his drawing on was 21ft long and weighed four tons.
The port authorities could not save it so it was eventually shot to stop it suffocating.
Mr Ashton has now written down the story behind the picture for his family and has no intention of parting with it.
He added: "I feel as though the picture belongs to John.
"It's not mine. "I have no intention of ever selling it, although it is probably quite valuable. John and I were very close.
"We were friends from about the age of seven. We knocked around together and went to youth club, scouts and the church choir. The drawing was done when I was about 12 and he was 13. People forget that he was just a normal human being before all the fame happened."
David Ashton will be a special guest on Spencer Leigh's Radio Merseyside programme On The Beat tomorrow evening starting at 6.30pm.
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