The "Transformers" stunner only began dating the rapper/actor at the start of the summer, but they quickly became inseparable and Fox even featured on Kelly's latest album, "Tickets to My Downfall", which was released in late September.
On the track "Banyan Tree (Interlude)" - an apparent nod to Costa Rica, where the couple first crossed paths - she mentions getting ink dedications to one another, saying, "It was just four months ago that we were right here and I met you. That's not possible."
"You just got my initials tattooed on you. I just got your nickname tattooed on me."
However, it wasn't until Sunday night (November 22), when the pair posed together at the Los Angeles prizegiving, that Fox showed off her scripted skin art, which features the words, "el pistolero" - the Spanish translation of gunfighter, along her collarbone.
Kelly, real name Colson Baker, has yet to reveal his tattoo for Fox.
The stars met on the set of their upcoming film, "Midnight in the Switchgrass", and Fox recently gushed about the flood of emotions she experienced when she first gazed into his eyes.
"I looked into his eyes (and) I felt the most pristine, most gentle, most pure spirit," she told Nylon magazine. "My heart shattered immediately."
Prior to dating Kelly, Fox was married to actor Brian Austin Green, the father of her three young sons. They are currently estranged.