"They are no longer dating," the insider said. "It was really a location challenge. She has been in Europe shooting 'Game of Thrones' and he is based in California, so it was hard to make it work despite the distance. They have remained friends."
MacFarlane, 39, is the creator of "Family Guy," as well as a film writer and director.
Clarke, 25, can now be seen on Broadway in "Breakfast at Tiffany's."
Celebrity Couples of 2014 [PHOTOS]