Michael Bay insists 'Transformers 4' isn't a reboot.

The director quashed claims the next instalment of his futuristic robot franchise would be a complete reinvention and insisted the film was simply going to feature a ''redesign'' of the alien machinery.

He told Forbes magazine: ''No, that's wrong. We keep the Transformers the way they were, it's just four years later. There's a reason the Transformers are redesigned. We're trying to broaden the franchise and give it more places to go.''

Up-and-coming actor Jack Reynor has been cast as the lead alongside 'Ted' star Mark Wahlberg, and Michael admits he wanted to leave the films with a fresh cast and an exciting new outlook before moving on to other projects.

He said: ''We're going to start off smaller. There's a brand new cast. To freshen the franchise we've redesigned everything from top to bottom. The history of the first three movies is still there, we start four years later and there's a reason why we're meeting a new cast.

''Mark is really excited about it and it's a great redesign. I said that 3 was going to be my last one. Paramount was letting me do 'Pain & Gain' and the Transformers ride was opening at Universal and it was bittersweet to think of passing it off. I wanted to set it up on a really sure footing and to bring someone else in on that, it would have been overwhelming.''