MADRID (AFP) - When Spain's Princess Letizia is crowned queen on Thursday, she will surrender a tiny corner of privacy that has allowed her to sneak out with friends to cafes, plays and a string of indie rock concerts.

The elegant 41-year-old royal's secretive mingling with the public, often with a few girlfriends and in non-regal attire, has provided rich fodder to 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 huge FIB rock festival in the eastern beachside town of Benicassim in July last year.

Following King Juan Carlos' abdication announcement on June 2, however, the life of the taxi-driver's granddaughter is set to be transformed.

Letizia's outings really began to make headlines last year in gossip media, which alluded to rumoured problems in her relationship with Prince 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 to that of the king's household", Apezarena said.

Letizia has learned a lot since she married the future King Felipe VI 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.

In her private life, Letizia now takes Felipe into 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 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 the king's abdication announcement, 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. 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," he said.

After Letizia's husband is sworn in as King Felipe VI on Thursday, the couple will be driven through Madrid. Instead of jeans, Letizia will don a dress for the royal occasion that remains a closely guarded secret.