The Adolfo Dominguez dress belongs to the 2018 collection and is currently sold out.
The royal was also seen carrying a white handbag by Furla.
On this occasion, the queen opted for classic makeup with a dash of mascara.
She decided to keep her jewellery to a minimum, sporting a pair of gold hoop earrings.
Despite the warm weather, Queen Letizia let her hair fall straight down her shoulders.
Madrid reached temperatures of 38 degrees earlier today.
Fans took to social media to comment on her fashion choice.
Although some believed she was looking very chic, many thought the combination of a tweet dress and leather shoes wasn’t the most appropriate look for the warm weather.
“Very impractical outfit,” concluded another user.
As Honorary President of the Spanish Association Against Cancer, she attended today’s meeting despite the heatwave.
Fans also criticized her latest fashion choice, when she decided to wear heels as she walked along Camino de Santiago, the most famous pilgrims’ route in Spain.
Fans commented on her outfit and although some thought she looked like a “chic pilgrim” many were shocked by her footwear choice.