The golden rule of broadcasting: make sure your mic is off before you drop a reference to the potential new First Lady's assets.

ABC Breakfast presenter Virginia Trioli was left red-faced after she was caught commenting on Melania Trump's breasts while still on-air.

She was covering the US election around 10am this morning and likely assumed the feed had crossed to a break.

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Speaking of the viral photos of Trump staring at his wife's ballot paper, Trioli told her team - and all her viewers - that he was more likely "looking at Melania's t*ts".

Trioli had actually tweeted the image earlier, inviting viewers to caption the viral photo.

She went on to argue that those on social media who were Mr Trump supporters "should be subjected to an IQ test" before they voted.

Twitter users went into meltdown mode trying to warn her.