The X Factor judge met the British Prime Minister at the Pride of Britain Awards 2012 earlier this week, but she didn't recognise him.
The singer explained that she thought Tony Blair was still the Prime Minister, and even asked one of Cameron's aides where Blair was.
"I didn't know who he was," Scherzinger told The Mirror.
"They said they were introducing me to the Prime Minister and he came over, and I was like, 'Where's Tony Blair?' I thought it was still him.
"Someone had to tell me. I was a real ass."
Yesterday, Scherzinger was spotted wearing an Asda uniform in honour of her X Factor act Jahmene Douglas.
Watch the X Factor judge talk to Digital Spy below:
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