Just one day before their death, Rob and Michele Singer Reiner were celebrating the holidays at Conan O'Brien's Christmas party... when a fight broke out between the father and his son Nick. Family sources told TMZ on Monday that at the former late-night star's party on Saturday night, Rob and Nick got into a "very loud argument." It's unclear what they were arguing about, but it was so loud, several folks overheard the commotion. Soon after, Rob and Michele left the party. It's not known whether their 32-year-old left, too.