updated 10/08/2012 AT 2:00 PM ET
•originally published 10/08/2012 AT 2:20 PM ET
Theroux was visiting the actress – who’s currently filming We Are the Millers in New Mexico – when Aniston, 43, reached up to touch his face, baring the bauble.
“Everyone is really excited for them,” a source told PEOPLE at the time.
“It’s amazing to see how happy Justin makes Jen, and everyone was always hoping that he would propose.”