Found this on MSNBC:
MSNBC:
Anthony Edwards will reprise the role of Greene, who died of a brain tumor at the end of the 2002 season, in flashback scenes in the Nov. 13 episode, NBC announced Thursday.
Dr. Greene will be shown with other characters from the show’s past and during an encounter with series newcomer Dr. Cate Banfield (Angela Bassett), an attending physician at County General, the network said. The names of the other returning “ER” alumni weren’t released.