This is one of my favourite puzzles. One seems to end up in a tangle quickly, going back and forth between generations.
See if you can solve it without a hint.
Some people find it helpful acting out the below scene & pointing to an imaginary painting. (This should be done at own risk, as people may think you are a bit of a nutter)
Harold stands before a painting and says:
“Brothers and sisters, I have none. But this man’s son is my father’s son.”
Who is the man in the painting?
The man in the painting is Harold’s father.
Step 1: Start at the end: “my father’s son” -> this is Harold
Step 2: “this man’s son” is [Harold]
Thus it must be his father.