An Australian ad agency working with National Australia Bank won the top PR prize at the Cannes Lions awards festival in France Monday, the second year an ad shop won the Grand Prix honor.

The campaign, created by Clemenger BBDO Melbourne, was kicked off by a tweet intended to look accidental and sought to portray an NAB “break-up” from the country’s three other large consumer banks in the wake of the global economic crisis, as Australian consumers have suspected the top four of fixing fees and stifling competition (video/details of winning campaign).

The PR jury was led by Fleishman-Hillard president and CEO Dave Senay, who said 105 entries were shortlisted for honors. Ten won Gold, 13 Silver and 15 Bronze Lions.

Senay told reporters after the winners were announced that whether agencies are focused on PR or advertising isn't as important "in an era where the labels matter less and less."

The Australian firm, estimated the PR campaign, which also included full-page break-up letters in newspapers and videos of NAB bankers breaking up with other banks, generated $5M in earned media in one day.

Gold Lion winners in PR for the U.S. included IBM’s Watson campaign with Ogilvy & Mather, and TBWAChiatDay’s AIDS awareness push, which won two Gold honors.

Hill & Knowlton’s London office picked up a Silver Lion for a multiple sclerosis education effort, while Burson-Marsteller/U.K. won silver for a push for the Royal British Legion’s “Poppy Appeal” fundraising campaign.

The Kaplan Thaler Group, New York, won a Bronze Lion in the crisis category for its rollout of the new Aflac duck voice.

Complete list of PR Lions winners (PDF).

TBWA, with help from Fleishman-Hillard, won the top PR Lion last year (link, sub req'd) for a U.S. campaign for Gatorade.