"They blocked him when he tried to exit. Robert panicked, but then the alien monsters whipped off their scary headgear and revealed they were just three giggly Earth gal fans!" Contactmusic quoted a source as saying.
The girls were apparently wearing huge platform shoes to look taller and when the fans realised the 23-year-old actor was nervous, they removed their masks and asked for his autograph. The hunk, seemingly, thought the stunt to be funny and acknowledged the ladies.
The insider said: "Robert thought it was a hilarious stunt and gave the girls everything they wanted."