After the tip-off was given, Mr Brown was told and left the Auckland Town Hall to go home to Manukau where he told wife Shan about the affair. He was later joined by his political adviser David Lewis.
That evening, Mr Brown cancelled a mayoral debate hosted by the Takapuna North Rotary Club at Spencer on Byron hotel in Takapuna, citing a bad cold.
It was a very tough week for the Brown campaign, the source said, not knowing when or if the affair would come to light.
But as about two-thirds of the votes had already been cast or were in the mail at the start of the final week of the postal ballot, the Brown camp did not believe the affair being made public would materially effect the result.
When Mr Slater did reveal the affair on his Whale Oil blog at 2pm on October 15 - three days after the election result - Mr Brown was at home, resting and recuperating from the campaign and a lingering cold.
Prime Minister John Key said on Monday the National Party was not involved in the scandal.
Luigi Wewege, 28, who belongs to the National Party youth wing and was a member of Mr Palino's mayoral campaign, was in a relationship with Ms Chuang and wanted her to expose the mayor's infidelity.
Mr Wewege has gone to ground since a Facebook message exchange he had with Ms Chuang was revealed by the Herald last week.
- Additional reporting: Morgan Tait
How it unfolded
• October 6: Bevan Chuang meets journalist Stephen Cook to discuss a story. She doesn't provide evidence, so Cook says there is no story.
• October 7: Late morning/early afternoon: National MP tips off Auckland councillor there's going to be a sex scandal involving Len Brown. Councillor informs Brown camp.
Afternoon: Len Brown goes home and tells wife Shan Inglis of affair.
Evening: Len Brown cancels mayoral debate in Takapuna, citing a bad cold.
Blogger Cameron Slater writes a post urging people to vote for John Palino saying Brown likes to cast a "glad eye over Asian beauties", a veiled reference to what would unfold.
• October 12: Len Brown defeats John Palino for the mayoralty and Chuang fails to be elected to a local board.
• October 14: Chuang sees Cook again to tell him about the affair. He works through the night writing up her story.
• October 15: Cook takes Chuang through affidavit which she swears in Auckland District Court. Hours later, Slater breaks the story on his website. Brown at home when the story breaks.