A sighting of Julianne Moore filming a scene of 30 Rock with the show’s debonair star, Alec Baldwin, has whipped up the rumour mill.

Moore, it is speculated, could just be the mystery girlfriend Baldwin referenced when he said: “I won’t say who it is, but someone very near to us who may be coming on to play my girlfriend for four episodes.”

Baldwin was talking of his character Jack Donaghy. According to a witness at the Rockefeller Center, where the scene was unfolding: “During the time I saw them they were in between takes, so not really saying anything of note. They looked very chummy though! No one else from the cast appeared to be there.”

Moore, 48, has been nominated four times for an Oscar.