Donald Trump's chief of staff Mark Meadows has returned a positive test for Covid-19.
The shock diagnosis comes as the US anxiously awaits the result of the presidential election, and on the nation's biggest day of new coronavirus cases since the pandemic began.
Mr Meadows is a key member of the Trump campaign – and in recent days has thrown his support behind Mr Trump challenging the vote counting in several battleground states.
CNN's Chris Cuomo said Mr Meadows' diagnosis demonstrates Mr Trump's "nonchalance" toward the Covid-19 pandemic, despite himself – and a number of other White House staffers – testing positive back in October.
According to reports, Mr Meadows – who rarely wears a face mask – was not wearing one on election night at the White House, where he interacted not just with the President but Ivanka Trump, her husband Jared Kushner, and Mr Trump's son Donald jnr.
One White House aide told CNN that officials are now "alarmed", given Mr Meadows has been around other staffers and Mr Trump's family members while potentially contagious.
Mr Meadows, who "abided by President Trump's efforts to play down the coronavirus throughout the summer", The New York Times reports, tested positive to the virus on Wednesday.
A second White House campaign aide, Nick Trainer, is also infected.
It comes just seven weeks after Mr Trump, First Lady Melania Trump, and his youngest son Barron – as well as at least 30 others – contracted the virus at an event celebrating the nomination of Supreme Court Justice Amy Coney Barrett.
Just nine days before the presidential election, Mr Meadows somewhat changed his tune, telling CNN the US was "not going to control the pandemic … because it is a contagious virus just like the flu".
"What we need to do is make sure that we have the proper mitigation factors, whether it's therapies or vaccines or treatments to make sure that people don't die from this," he said.