A man's home is his castle. Or, in Robert De Niro's case, a billionaire actor's illegal penthouse atop his swanky seven-story TriBeCa hotel (the $600-a-night Greenwich Hotel), is his castle.

Either way, the Taxi Driver tough guy, even after being told last year to change the building's facade, isn't about to sit by and let the Landmark Preservation Commission get in the way of the penthouse of his dreams (complete with marble bathtubs and a handmade brick exterior). Apparently his lair is 1,100-square-feet bigger than the design the LPC had originally approved and doesn't fit in with the neighborhood's industrial-style rooftops.

While the actor apologized for any "mistakes" and asked the commission for retroactive approval of the designs, he has yet to lift a finger and make any changes, the Post learned—an LPC spokeswoman said "We don't really know what the cause for the delay has been."

The commission hasn't set a deadline date for De Niro to make changes to his penthouse, but could order the structure be torn down, to the tune of more than $1.5 million.