Fox, 35, decided not to attend the movie premiere at the last minute due to concerns over COVID-19. Meanwhile, Kent, 30, appeared to diss Fox for the move. Kent is engaged to the movie's director Randall Emmett.
According to the Daily Mail, the "Vanderpump Rules" star appeared to first jab Fox by posing in front of one of the posters for the movie and covering up Fox's credit with the words: "So excited for this!"
The Instagram Story has since been deleted.
Fox released a statement on Monday announcing her absence from the premiere, which was held at Regal LA Live in downtown Los Angeles later that night.
"Due to the recent California mask mandate and rise of COVID cases, Megan Fox will no longer be attending the premiere tonight. We appreciate your understanding," a statement obtained by Variety said.
Kent showed up to the premiere in a glittery green low-cut dress. And on Tuesday, the reality TV star appeared to take another subtle dig at Machine Gun Kelly's girlfriend by praising the film's stars Caitlin Carmichael, Lukas Haas, Emile Hirsch in addition to her husband.
"To our sweet Caitlin: What a joy it was seeing you on the big screen last night. You are so stunning, & your talent is unparalleled. I can't wait to see what your future holds. Thank you for being a part of Rand's directorial debut. We love you!!!" Kent wrote to Carmichael.
She went on to call Haas a "f--king star" and described Hirsh as an "incredible actor."
"& to my soulmate. My life partner. My baby daddy. Congratulations. I am so proud of you. You did it, boo," Kent concluded to Emmett along with a photo of the two at the premiere.
Kent did not post a tribute to Fox, however.
Earlier this week, Emmett discussed Fox's chemistry with Machine Gun Kelly. The pair made their relationship public in May of 2020.
"There was magic in that room, 100 percent," Emmett told Yahoo! Entertainment in an interview published on Monday. "I sat there behind the monitor, and there were takes where I was so mesmerized by their performances that I would forget to say 'Action!' Megan sometimes had to be like, 'Randall, are you going to call 'Action?' I was like, 'Oh my god — my bad!'"
Emmett clarified that he didn't think about "anything else" going on at the time.
"As a director, I felt, 'Wow, there's some real magic happening there,' but I didn't see any more than that," he explained.
"They're both incredible actors, and their chemistry was flawless. I was just looking at them and thinking, 'Wow, that was a great scene,' but didn't really think about anything else."
Fox and Machine Gun Kelly reportedly began seeing each other while the two were filming the movie. Fox, who was married to actor Brian Austin Green at the time, went on to file for divorce in November.