Do we ever see Krusty's mother? If the answer is no, the consider the following theory.
- Homers physical appearence is gained from his father. (We assume)
- Krusty is drawn very similar to Homer, in physical appearance.
- Abe is known for "whoring" around. Note the half brother Earl (?).
Consider this. Abe had an affair with Krusty's mother. Krusty's father, being an upstanding Rabi, either did not know about the affair, or decided to cover it up. Therefore, Homer and Krusty are brothers.
Just a thought... perhaps if a writer of the simpsons is reading this... they could consider this at some point?
The idea came to me watching tonites episode, as Homer and Krusty walked down the beach next to each other.