King Felipe VI attended the ceremony, which saw them dine with Swedish, Danish and Norwegian royals.
However, Letizia did not attend the ceremony and refused to let her daughter Leonor, Princess of Asturias, go as well, it is claimed.
She suggested the Spanish Queen “did not want Leonor to attend” the occasion over concerns about image.
Queen Letizia set a rule for her daughter to not have royal friends
Leonor, Princess of Asturias, has returned from a Welsh boarding school
Writing for website lecturas.com, Ms Eyre said: “Letizia did not want Leonor to attend.
“Posing with the other heiresses of European thrones in long dresses and crowns in an ostentatious palatial setting would not be the best starting point for a monarchy that pretends to be simple and democratic.”
The expert added the event itself was not the issue, but the image conveyed by dining with other royalty holds the Queen back from attending similar events.
Ms Eyre added: “To dispense with all superfluous luxuries has been one of Letizia’s workhorses in the eight years that her husband has been on the throne.”
Pilar Eyre said Letizia ‘did not want Leonor to attend’ a birthday party for a Norwegian royal
Pilar said Letizia’s has tried to ‘dispense with all superfluous luxuries’ since becoming Queen
The expert said: “She has made an effort to dismantle one by one the habits of the previous queen, with whom she barely has any contact.
“Letizia is now in a position of security and confidence in which she does not hesitate to assert her opinion and her conception of the institution.”
Princess Alexia of the Netherlands also attends the boarding school.
Louise Callaghan, alumna who went on to serve as a foreign correspondent for The Sunday Times, explained: “(The school) is a bit like a hippie Hogwarts: full of oddballs who think they are fighting the forces of darkness.
“There are also ghosts.
“Lady Stradling haunts the history tower, and the smell of lavender and a lilac mist precedes her apparition.
“The ethos is, broadly, that people from all over the world can get along if you shove them together in a castle.
“That much we proved, some very passionately.”
Additional reporting from Maria Ortega
Source: EXPRESS CO UK