Shia Labeouf, left, and Megan Fox join director and producer Michael Bay at the Berlin premiere of Transformers: Revenge of the Fallen in June. Shia Labeouf, left, and Megan Fox join director and producer Michael Bay at the Berlin premiere of Transformers: Revenge of the Fallen in June. (Maya Hitij/Associated Press)Michael Bay has confirmed that a third instalment of his blockbuster Transformers film franchise will arrive in 2011.

"Well it's official: we have a great Transformers 3 story," the director said on his official website Thursday. "The release date is now July 1st 2011. Not 2012."

Young stars Shia LaBeouf and Megan Fox are slated to return for the third film, which follows 2007's Transformers and this summer's Transformers: Revenge of the Fallen.

Despite a mostly rough ride from critics, the first two films have grossed more than $1.5 billion US worldwide.

Ehren Kruger, one of the writers for the summer sequel, is to pen the script for the third film.

In interviews, Fox has often mocked her participation in the lucrative franchise and was recently targeted in an open letter by several longtime Bay crew members after trashing the director-producer as "a nightmare to work for.

She was also mentioned in an apparent tongue-in-cheek postscript to Bay's message.

"P.S. Megan Fox, welcome back," Bay wrote. "I promise no alien robots will harm you in any way during the production of this motion picture.

"Please consult your physician when working under my direction because some side effects can occur. … As some directors may be hazardous to your health, please consult your doctor to determine if this is right for you."