A few years back my oldman bought a painting for me at an auction. Some local cheap one.
He decided to reframe the painting. Behind it he found a John )clinton maybe) sketch of a dog (do you know the artist who was famous for sketching hroses etc from UK)
He didn't know if it was real or not. He suspected it was a copy but why was it behind the painting/
When I left I gave it back to him and he has never had anyvody look at it.
Odd thing to do but the old man says that he doesn't care the story is good enough.