Joker as Batman's Dad?

Here's a bit of fan-fic that I came up with...

What if the Joker is actually Batman's dad.   

A young Bruce Wayne is walking home from The Mask of Zorro with his parents, Thomas and Martha Wayne.  They take a shortcut through what would later be called Crime Alley are shot and left for dead.  All for Thomas' wallet and a string of pearls.

A traumatized Bruce safely waits in police custody to be picked up by his butler, Alfred.  Thomas and Martha are whisked away to a private hospital owned by the Waynes.  Martha dies en-route.  However, Thomas survives but remains comatose.  For fear of follow-up and possible kidnapping of Bruce, his security team acts on Thomas' established instructions of keeping him in hiding during his recuperation.  But he remains in the coma for years. Bruce grows up an orphan, raised as best as he can by his only family left, Alfred Pennyworth.

Meanwhile, Thomas' condition remains unchanged.  He becomes pale from lack of sun, and his hair turned green due to dysfunction in his kidneys due to the gunshot.  When he finally awakens, gaunt and thin, he learns of his wife's death and that his son Bruce grew up without parents and has left to travel the world without an explanation to anyone...even Alfred.  This heaping loss, as well as residual brain damage from the accident along with years of solitude drives him mad.  He sees the whole thing as one cruel joke.  And his suffering is the macabre punchline.  He sees laughter as the only distraction from feeling the unfathomable loss that is the hole in his life that his family once held.

He becomes obsessed with wanting to share the joke with the world.  He is desperate for anyone to connect with.   When Batman emerges in Gotham, the Joker feels a bond immediately.  He doesn't realize on the surface that the Bats is his son...but in Batman, he sees Martha's eyes.  Deep down on some unconscious level, the Joker recognizes him as his own flesh and blood.  He sees a kindred spirit who, clearly is looking for something to fill his emptiness, too.  

So, he begins his endless quest to help the Batman.  To make his son finally cheer up and laugh.  At any cost.