Although Apple, which is notoriously secretive about its corporate structure, declined to comment on Seitz's appointment, it is understood that she has taken the title of senior PR manager, a role that functions as deputy to Apple European corporate communications director Alan Hely.
Seitz's decision to move to Apple, whose UK consumer account she had handled at Bite for eight years, emerged this week as the company shifted its European headquarters from Paris to London.
This Tuesday the company was busy setting up a new nerve centre above its 22,000sq ft store in London's Regent Street, which was opened last November.
Seitz's remit is to co-ordinate Apple's PR activity across Europe.
The move to the heart of the UK capital's shopping district is another indication of Apple's shift towards being a style-conscious purveyor of consumer electronics. Its origin is in the manufacture of specialist personal computers.
The phenomenon of Apple's iPod, the personal stereo on which a listener can store hundreds of songs, has transformed the company's fortunes.
Apple reported a six-fold increase in profits of £150m for the first quarter of this year on the back of a revenue rise of 70 per cent to £1.8bn, £575m of which was iPod related.
The iPod craze has already created a powerful brand message, often referred to as the 'halo effect', that has seen iPod owners buying other Apple products such as the new Mac Mini computer.
Seitz joined Bite from Talk Loud PR in 1997. Last year she returned from maternity leave to move across from her role as Bite MD to become consumer MD. The shift made way for former Countrywide Porter Novelli managing director and Fleishman-Hillard CEO Barry Leggetter, who was appointed as Bite chairman.
Leggetter said this week that Seitz's responsibilities had been handed to board director Rachel Bachmann in the position of head of consumer.