A combination of factors triggered the unprecedented blackout that left Spain and Portugal without electricity for several hours last year, a new report has found.

On 28 April 2025, shortly after midday, the Iberian peninsula's electricity supply was shut down, causing widespread chaos, cutting internet and telephone connections and halting transport links.

The outage hit schools, universities, businesses and public buildings, and a small area of southern France near the Spanish border was also affected. Some areas did not recover power for 16 hours.

The outage originated in Spain, and Portugal was also affected because of the two countries' close interconnection.

Entso-e, the European Network of Transmission System Operators for Electricity, described it as "the most severe and unprecedented blackout that had occurred in Europe in the past 20 years, with a major impact on citizens and society as a whole" in Spain and Portugal.

In October, Entso-e, which has been investigating the incident, presented a preliminary report on it.

In its final findings, it has now said that there was no single cause and instead there were "multiple interacting factors" which led to the blackout, linked to the Spanish network and the companies that use it.

An uncontrolled, sudden increase in voltage in the system "on a day with multiple concurrent phenomena" led to instability and "cascading generation", it said.

In its diagnosis, the report found that voltage controls of local energy generators were not fully aligned with those required by the grid operator. In some cases, manual control of voltage meant that the system responded relatively slowly to changes in the network.

Also, the Spanish grid's voltage range is greater than that of many of its neighbours, giving it limited margin in the case of voltage surges that might lead to a disconnection.

"The reactive power assets in the system were not able to address the sudden voltage rise," the report said.

The blackout and the government's failure to provide an immediate explanation for it led to a political debate which saw some critics accuse the authorities of incompetence and query Spain's energy model.

Close to 60% of the country's electricity is generated by renewable sources. The opposition suggested that the Socialist-led government should reconsider its plan to phase out nuclear generation.

The electricity outage also caused a dispute between the grid operator, Red Eléctrica, and private energy companies over who was responsible.

The Entso-e report steered clear of such issues, insisting that its investigation did not aim to apportion blame. But it did issue recommendations aimed at preventing a similar incident from occurring. They included improving coordination between transmission operators, distribution operators and other parties in the energy system.

News of the invitation emerges after the monarch acknowledged "a lot of abuse" during the Spanish conquest of Mexico.

King Felipe appears to have helped thaw frosty relations with Mexico while reviving a fierce debate over events 500 years ago.

The child did not see a doctor until she was six - and had not had any vaccinations, Italian media say.

Madrid cites humanitarian and economic reasons to give undocumented workers legal status.

Spain's prime minister delivers a strong rebuttal to US President Donald Trump's threat to end trade with his country.