The elegant royal's secretive mingling with the public, often with a few girlfriends and in non-regal attire, has provided rich fodder for the Spanish gossip media.
The blonde-haired former television news presenter was snapped in jeans and black leather jacket in April last year outside a Madrid concert by US alternative rock group Eels.
A few months earlier, she joined spectators at a concert by 1990s Spanish indie group Los Planetas.
And she is apparently a big fan of Las Vegas band The Killers, seeing them in Madrid in September 2012 and again at the FIB rock festival in the eastern beachside town of Benicassim in July last year.
The life of the taxi-driver's granddaughter is set to change dramatically, however, now that her husband Felipe has been sworn in as king, making her Spain's first "middle-class" queen.
She stood beside him at Thursday's swearing-in wearing a simple knee-length white dress and white jacket.
– 'Something was not right' –
Letizia's outings when she was princess really began to make headlines last year in gossip media, which alluded to rumoured problems in her relationship with Felipe, said royal watcher Jose Apezarena.
"The royal household let the princess know that her repeated outings gave the impression that something was not right," said Apezarena, author of "Felipe and Letizia. The conquest of the throne", published this year.
Born on September 15, 1972 into a middle-class family, Letizia Ortiz was already in her 30s when she met Felipe, who she married in 2004. A divorcee, she had already forged a career in television news and had her own tastes.
She took on her new role "like a real job and applied her previous work methods", Apezarena said.
Letizia is described by her circle as having been "responsible" and a "perfectionist" since her youth, he said.
As the spouse of the heir to the throne, she took part in weekly meetings of the royal household.
Not coming from royalty and still in touch with old friends, she brought a fresh point of view, "a different sensibility from that of the king's household", Apezarena said.
Letizia has learned a lot since she married Felipe a decade ago, and she knows being queen will entail new responsibilities, said Cote Villar, journalist at the conservative Spanish daily El Mundo.
"She has many interests. She is a women of her time, who has studied a lot and is cultured," said Villar.
"Since the king told them in January that he was going to abdicate, she has not had any more outings like that. It is the best proof that she is perfectly aware of what it means to be queen," she said.
– Cool and distant –
In her private life, Letizia has taken Felipe on to her "terrain", said Villar. "He now goes to see films and plays he would never have seen," she said.
Despite the touch of modernity Letizia lends to the palace, she still often appears tense in public, fearing she will make a gaffe and "too worried about what people will say about her", the journalist said.
Seen as cool and distant by some, she is the least popular of the tight circle of the royal family.
A poll published on June 9, a week after Juan Carlos announced his abdication, showed a slight improvement, however, with just over 54 percent of respondents seeing Letizia in a favourable light.
Since Juan Carlos's abdication announcement on June 2, the Spanish media have become "much friendlier", said Villar.
Her accession to the throne could improve her image yet further, said Apezarena.
Letizia has avoided major gaffes and her readiness to listen has earned her the respect of many with whom she is in contact, despite a sometimes "excessively critical" Spanish media, the author said.
"Being princess is not the same as being queen," he said. "They are going to see her in a new light and certainly with a bit more understanding, because when you're a candidate you're under scrutiny."