After the tremendous success of 2007's Transformers and 2009's Transformers: Revenge of the Fallen, together grossing over $1.5B, the question of what happened to Megan Fox's character Mikaela Banes in Transformers: Dark of the Moon remained. At the end of Transformers 2, Mikaela and Sam's (Shia LeBoeuf) relationship seemed strong. Sam Witwicky's near-death experience was the catalyst that helped Mikaela finally express her feelings for him. When Sam was revived and declared his love, the characters were on track for a happy start to the third installment.
Transformers: Dark of the Moon, however, proved to diverge from the expected. Once the film was released, there was no Mikaela to be found. Also, the Autobots, desperate to protect themselves, even resurrected Sentinel Prime (Leonard Nimoy) to help them beat the Decepticons. This was only the beginning of changes to the beloved franchise. Even Sam himself did not return for Transformers 4.
Sam's love interest was quietly replaced by Carly Spencer, played by model Rosie Huntington-Whitely. There was little explanation for why Mikaela and Sam ended their relationship, besides a mention from one of the Transformers that Sam "got dumped." The fact that their story ended so abruptly left plenty of room for speculation about where she had gone and why. Questions were raised about Fox's quick exit, including rumors that Fox left the franchise because she lost interest in it. Stories circulated that during the filming of Transformers 2, director Michael Bay ordered Fox to simply "be hot" or "just be sexy" in certain scenes. Blaming and sidestepping, the real reason she had left was coming from both sides. The film's refusal to address her absence on screen did not help matters. The truth was revealed that Fox was fired from Transformers 3.
Bay asserted that he simply asked her to follow directions and show up on time, standards for which he playfully apologized. After hearing Fox likened Bay to both Hitler and Napoleon, Stephen Spielberg urged him to fire her immediately. A Transformers 3 crew member also shared (via The Guardian) that he felt she was "dumb as a rock" and not talented enough to work on the film. Fox then shared (via Cosmopolitan UK) that being fired from Transformers 3 was "absolutely the low point of my career." It appeared the rift between Bay and Fox could never be healed. Neither said publicly, though, that they would never again work together and in 2014, they teamed up again to make blockbuster Teenage Mutant Ninja Turtles and 2016's Teenage Mutant Ninja Turtles: Out of the Shadows, proving their relationship was indeed salvageable.
The public and abrupt exit after Transformers: Revenge of the Fallen signaled a trajectory change for Megan Fox's career. She has rarely been cast in roles larger than the ones for which Bay hired her. Her next most successful venture outside of the Bay productions was cult comedy Jennifer's Body. Fox blamed her immature attitude and behavior for the loss of her relationship with that franchise. Fox has since had three children with ex-husband and 90210 alum Brian Austin Green and got engaged to rapper Machine Gun Kelly in January 2022. Fox is starring in Expendables 4, slated to be released sometime in 2022. Granted, Transformers also marked an end for LeBoeuf and Huntington-Whitely's roles, so it's unlikely Mikeala and Sam would have had much of an on-screen future together if they stayed together.