Theron was spotted arriving at Los Angeles International Airport today wearing demin-on-denim and sporting a shiny new bauble on her left ring finger, thereby immediately setting off fresh round of speculation that Penn had popped the question.
Reps for the actors have not responded to requests for comment, but we have our own doubts about the significance of this particular piece of jewelry.
In pics obtained by E! News, Theron was wearing an 18-karat yellow gold Anita Ko Leaf Ring, which retails for $4,900.
That just seems a little...casual for an enagagement between wealthy, glamorous Oscar winners.
(And you can see it even better in the pic where she tried to shield her face with her white blazer, leaving her ring hand exposed for the camera.)
But in general, romance burst into full bloom pretty quickly for Penn, 53, and Theron, 38, who just coupled up toward the end of last year.
"Sean and I have known each other for 18 years," Theron told Vogue for its May issue. "We were just really good friends and it's been slow going because you are aware that you could screw that up and lose it. We had to think about it. But at the end of the day, it was somewhat effortless."
The Mad Max: Fury Road star has never been married. Penn was married to Madonna for four years back in the 1980s and then divorced Robin Wright in 2010 after 14 years of marriage.
(Originally published on Thurs., July 24, 2014, at 5:47 p.m. PDT)