I was very shocked and saddened to receive a letter from France yesterday telling me of this news. He was killed instantly in the crash. Jean was working on a career in the US, had established an apartment in New York, and had representation in the US.
Count Phillipe de Montebello is the director of the Met and I believe their relationship is uncle/nephew. I'm working on verifying this. He was just 32 years old.
His web pages are still up:
http://www.portraitartist.com/demontebello