Megan Fox and her husband, Brian Austin Green, have reportedly decided to end their marriage for good by filing for divorce.

And according to speculations, Shia LaBeouf may purportedly be involved in the split of his former "Transformers" co-star and her husband.

"There were rumors that Shia LaBeouf and Megan Fox had a brief fling while filming in the second movie in 2008 while she and Brian Austin Green were on a brief break from their relationship," Celeb Dirty Laundry reported.

"Now rumors that Shia and Megan were hooking up again! Was that the final straw for Brian?"

According to a source close to Brian Austin Green, Megan Fox's husband is reportedly aware of her and Shia LaBeouf's alleged affair on the set of their movie.

"Brian has always been wary of what Shia's capable of," the insider told Dish Nation. "After he shot his mouth off about his on-set romance with Megan while Brian and her were split, there were significant issues."

According to the source, Megan Fox and Shia LaBeouf have been pretty close again these past few months.

"Megan started speaking to Shia about a year ago when the two of them were going through troubled times. Shia was off the rails, boozing heavily, and leaned on Megan for support," the source added.

"Her movie career was dwindling, and she went to him for advice after a series of film flops, and the two were able to comfort one another."

According to Brian Austin Green's friend, Megan Fox and her husband were also facing other troubles aside from the actress' closeness with Shia LaBeouf. But Megan and Shia's alleged affair was what purportedly drove Brian to end it with his wife.

"While they were having other problems as well - their careers being on a downward spiral contributed to their many arguments - it was her relationship with Shia that really hurt Brian," the insider continued.

"It was certainly a contributing factor to their split, and something that he found very difficult to get over."