Spanish media on Thursday hailed the decision to name King Juan Carlos's daughter Princess Cristina as a suspect in a corruption case, saying the unprecedented moved showed that nobody was above the law.
"If the decision to summon the princess had not been taken, the idea would arise of an attempt to distance the daughter of the king from any procedural nuisance by virtue of being who she is," centre-left daily newspaper El Pais said in an editorial.
In a ruling issued Wednesday, judge Jose Castro ordered the 47-year-old princess to testify at a court in Palma on the Mediterranean island of Mallorca on April 27 as part of his investigation into the case.
It is the first time a direct relation of the 75-year-old king has been called to appear in a court of law on suspicion of wrongdoing.
The case, which was opened at the end of 2011, is centred on allegations of embezzlement and influence peddling against Princess Cristina's husband, former Olympic handball player Inaki Urdangarin, and his former business partner Diego Torres.
The pair are suspected of syphoning off money paid by regional governments to stage sports and tourism events to the non-profit Noos Institute, which Urdangarin chaired from 2004 to 2006.
The judge's decision "undermines the monarchy" and "sinks an institution which has been cornered for the past 17 months", wrote centre-right daily El Mundo, adding Crown Prince Felipe's future was now more cloudy.
"The photo that will be taken on April 27... will exponentially multiply the number of stones on the path to glory of the heir," the newspaper added.
The princess -- the seventh in line to the Spanish throne -- is accused of allowing the lustre of her royal connections to be used by the Noos institute.
"Without prejudging how events will play out, it may be advisable that Princess Cristina, by her own initiative, ask the king to remove her from the line of succession to the throne," El Pais added in an analysis of the case, adding the judge's move was "inevitable".
"Fight fire with fire. The best way to prevent the head of state, who is under great pressure, from falling into an insurmountable decline is for Princess Cristina to appear as soon as possible before a court."
Conservative daily ABC, which is traditionally pro-monarchy, said called for the presumption of innocence to be respected.
"It is an affair that causes great harm to the monarchy and which must be seen in its proper proportions. If a member of the royal family must be judged, then so be it. But we can not raise doubts over the value of an institution that cements the unity of the Spanish nation," it wrote.