The campaign for the sugar-free drink, dubbed "bloke coke", will be created by Vallance Carruthers Coleman Priest, which was appointed to handle the launch in May. It will use TV, outdoor and digital ads and break shortly.
Coca-Cola flew Tweedy from Baden Baden in Germany, where she was with her fiance, Arsenal and England player Ashley Cole, to a photo shoot for a national press campaign.
The new brand is the first variant to the Coke range for 22 years - the last was Diet Coke in 1984.
The product is aimed at young adult males, who do not traditionally buy diet drinks, and will compete directly with Pepsi Max.
Coke Zero, which was launched first in the US last June, is also available in Canada and Australia.
The appointment of VCCP to the launch came as a blow to Mother, which recently picked up Coca-Cola's Fanta brand after its work on Fanta Z.
VCCP was appointed following its Diet Coke "Tort" campaign, which was created to give the brand a more unisex appeal.
Mother has worked on spots for Coke including a recent ad featuring a soundtrack written by White Stripes frontman Jack White, which only aired once on television.
Meanwhile, fellow wag Colleen McLoughlin is back to work to model for the new autumn/winter collection for George at Asda. She is understood to have secured a £3m deal to be the face of the label.
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