The First Lady looked typically fashion forward in the knee-length teal shift with a gathered neckline, all while supporting British fashion.
Samantha further shocked her fashion following by pairing the high street dress with an designer belt with a price tag of £196.
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The slim black embossed, mock-croc belt is by British designer Emilia Wickstead, one of Kate Middleton's favourite designers.
Samantha finished the outfit off with a Crombie-style black coa from Swedish retailer Cos.
The wife of David Cameron was attending the Conservative Party's conference. David said he was "incredibly proud" of her as she watched his make his speech in Manchester.
He was hailing national heroes who drive the economy by setting up their own businesses.
"To all those people who strike out on their own, who sit there night after night, checking and double checking whether the numbers stack up, I say I have so much respect for you," he said.
"I'll never forget watching Samantha do just that – winning her first customer, sorting out the cash flow, that magic moment when she got her first business cards printed. I was incredibly proud of her then, and I am incredibly proud of you now."
Samantha's first business involved designing shop window displays, interiors and packaging. One of her clients was luxury stationers. Smythson, a company of which she later became creative director.
When David entered Downing Street in May 2010, Samantha stepped down from the position into a part-time role.