But as the couple mark their 10th wedding anniversary on Thursday, Spaniards' affection for the princess — the first commoner in line to be queen in Spanish history — is lukewarm even though her husband's standing is at an all-time high.
Elegant and always poised, the granddaughter of a taxi driver remains untainted by a corruption scandal that has hurt the popularity of the monarchy, but is often criticized for appearing cold and distant in her public appearances.
"Letizia has always behaved very discreetly, in the background, and this possibly has robbed her of some spontaneity and distanced her from the public," said Jose Miguel de Elias, director of polling firm Sigma Dos.
"On the other hand it has caused her to avoid major blunders."
Just half of all Spaniards, 53.3 percent, felt Letizia had met their expectations and only four in 10 believed she was ready to be queen in a poll by the firm in 2012, when she turned 40.
And while one in two Spaniards have a high or very high opinion of the princess, according to the company's latest survey on the royals published in January, her level of approval has remained fairly steady since she married into the royal family in 2004.
By comparison two in three people have a similar opinion of her husband, a blue-eyed former yachtsman once described as Spain's most eligible bachelor, according to the UK's Independent newspaper.
Needs to smile more
Part of the problem is that the royal palace has relegated the princess to a secondary role to keep the focus on her husband, said Jose Apezarena, who has written a book about the royal couple.
"There was a certain fear that since she has a much greater capacity for communication she could eclipse the prince a bit so the decision was taken that, while she should not disappear, he is the important one in this couple," he said.
Letizia, who studied journalism in Madrid and spent time working on a Mexican newspaper after doing a Masters in Audiovisual Journalism, was a well-known face in Spain even before she joined the royal family due to her job as evening news presenter for Spanish public television channel TVE.
She covered the US presidential elecions in 2000, and reported live from New York during the World Trade Center terrorism attacks on September 11th 2001.
Letizia and Prince Felipe began seeing each other while she was covering the Prestige oil spill disaster in Galicia in 2002, but the relationship was kept under wraps for many months.
When, however, their engagement was announced in 2003, she was described as a "queen for the 21st century". And while some conservative elements frowned on the Prince's choice of a divorcée for a wife, experts noted that her first wedding had not taken place in a church and did not, therefore, qualify as legitimate.
Photo: Christophe Simon/AFP
She has attended just 190 official acts on her own since she married the prince, according to a tally by El Pais newspaper, but has been to 1,516 official acts together with her husband. At the latter, her role is usually limited to listening attentively with a serious expression as he speaks.
"Letizia has a difficulty in that she is too conscientious. The prince has on occasion commented that Letizia needs to smile more," said Apezarena.
"She is very dedicated, very demanding with herself, she is conscious of what she has to do and that has caused her to come across as a bit serious or even a bit hard. But she does not want to act differently from how she is."
Married previously to a writer and high-school literature teacher, Letizia gained an enduring reputation for having a strong character — and more than a few detractors — at her official engagement presentation.
When Felipe — who has confessed to celebrity magazine Hello! that he is also considered too serious by some — interrupted her as she explained how she would gradually leave her job at TVE, the future queen famously told him: "Let me finish!"
"I think she lacked a deft touch, not because a woman should be docile but because she should respect the protocol of a monarchy. That surprised people," said Jaime Penafiel, a veteran royal watcher and former editor of celebrity magazine Hola, who is a fierce critic of the princess.
"She has remained exactly the same during these 10 years," he added.
But while the princess may be seen as somewhat distant, celebrity magazines report a spike in sales when they put her on their covers and frequently publish images of her casually dressed as she shops for fruit or at rock concerts with her husband, or alone.
The couple, who have two young daughters, have kept their distance from Felipe's sister Cristina and her husband Inaki Urdangarin, who since 2010 have been embroiled in a graft inquiry, a rare embarrassment for the royals.
And Apezarena says that despite her flaws, he believes Letizia deserves to be held in higher regard by the public.
"Has she made any major mistakes? Nothing important," he said.