The European royal had pinned the ends of her hair underneath to create the illusion of a bob.
It's a trick fashionistas has been showcasing for years by tucking their ends into a high-necked jumper or coat. Lately, it has caught on with celebrities. Taylor Swift, Nicole Richie, Selena Gomez, Kate Beckinsale and Elizabeth Olsen have all tried the trend.
Letizia was attending the Young Businessman National Awards in Madrid, accompanied by her husband Prince Felipe.
She teamed the on-trend hairstyle with an off-the-shoulder black lace dress.
The dress will be familiar to fans of the Spanish royal. Letizia, who is known for her love of recycling outfits, has worn the creation by her favourite designer Felipe Valera several times before.
Letizia first debuted the designer dress in June 2012, when she added a state dinner held in honour of their visit at the Queluz Palace in Quelez.
She paired the gown with an elegant, side-swept chignon, nude shoes and a black box clutch.
In September of the same year, Letizia celebrated her 40th birthday. She marked the milestone with a set of family photos showing her wearing the beautiful dress as she poses alongside her husband and their two daughters Princess Leonor and Princess Sofia.
In November 2013, Letizia and her husband visited Miami for an official tour. For the Untied States and Spain Council Forum dinner, she wore the dress once again, pairing it with pointed black court shoes and a satin clutch bag.