Rocstar / Dmac / Fame Flynet 1 / 11
Rocstar / Dmac / Fame Flynet 1 / 11

Shia LaBeouf and his longtime girlfriend, Mia Goth, are engaged, according to a new report.

The engagement writing has been on the wall for a while.

Last February, Shia referred to his lady as his fiancée during his live-streamed performance art project #Elevate, for which he spent 24 hours riding an elevator, one of several "performance art" exhibits he's been involved with over the years.

A source also told Us Weekly that earlier this month the couple was at a Los Angeles supermarket and told the cashier that they were set to get married.

The onlooker said that Mia was sporting a large diamond sparkler on her engagement finger.

The couple has been dating off and on since meeting on the set of "Nymphomaniac: Vol. II" in 2012. They first sparked engagement rumors in March 2015 when she stepped out to a Miu Miu show at Paris Fashion Week with a large diamond on her ring finger.

Neither she nor LaBeouf publicly have commented on the status of their relationship, but sources said they temporarily split last July.

The eclectic star was spotted holding hands with his "American Honey" costar Sasha Lane several weeks later last year. Around the same time he snapped at paparazzi after they taunted him about his "Transformers" costar Megan Fox, who had just announced her divorce from Brian Austin Green.

However, shortly after that, things appeared to back on with Mia.

Considering how private he's been, don't expect Shia to publicly comment on the engagement news anytime soon.

In 2012, Mia spoke of what a perfect date was. "Maybe just stay in and cook and watch a great movie," she told I-D Magazine. "I'm obsessed with film."

Shia has been known to take his craft very seriously, as well, so this may be a match made in marital heaven. If nothing else, she has some blinding bling to rock through the ebbs and flows of their relationship.

Shia, of course, has been known for his bizarre -- sometimes bad boy -- behavior over the years.

Last November he watched all of his movies in 72 hours straight for a "performance art" project. After that he manned a call center to encourage people to "touch his soul."

In his aforementioned elevator stunt, he actually punched a guy in the face, at the man's request.