I'm not too familiar with his history (Because he's very -seldom used.), but I assume that it happened in the original Moon Knight run. I do remember getting an issue or two of his ooooold series, but that's all that I know about the character. Sorry. Anyone else? Bueller, Beuller?
Well, the original Moon Knight story in Marvel Spotlight is where Gregor comes from.
Anyway... with so many Gregors/Gregorys/Grigoris/etc. in the Russoff family, how do they even know about which anyone is ever talking about? This is my brother, Darryl. And that's my other brother, Darryl.
I'm pretty sure this is something the Handbook guys had to do because Gregor could not be the Baron. Jack is a pretty young guy when we first meet him.