According to the New York Post, it was an attempted assassination on the Long Island power broker.
Melius is at North Shore Hospital in New York where he's currently listed in stable condition.
"He is in surgery now and we are all waiting to see how he's doing. This is horrific!" his friend Stephanie Ovadia, host of the Stephanie O Show on 103.9FM in Long Island told Radar.
"Gary is known as one of the most charitable men on Long Island, we are all stunned by this. He always joined everyone at his castle, whether it was a celebrity wedding or a charitable event he made everyone feel at home."
Reports state Melius, 69, was shot while walking from the extravagant venue (where he also lives) to his car and the gunman immediately fled the scene.
The sprawling castle grounds have been known to host many celebrity and high-profile events — including the wedding of sexting fiend and politician Anthony Weiner and his wife Huma Abedin in 2010. The ceremony was officiated by former president Bill Clinton.