Wittenberg, an investment adviser, was on a business trip, Judy Katz, a spokeswoman for Peters, said Tuesday.
Three other people were killed in the crash, which occurred when the aircraft struck a high-voltage cable, police in Podgorica, Montenegro said.
Wittenberg married the Tony Award-winning actress in July 1996. They wed at the home of Mary Tyler Moore, a longtime friend of Peters.
Peters most recently appeared on Broadway in the 2003 revival of "Gypsy." Her other Broadway shows include "Sunday in the Park With George" and "Into the Woods." She won Tonys for her performances in "Song & Dance" and the 1999 revival of "Annie Get Your Gun."