Police in Bilbao have opened an inquiry into four Athletic Club players after the squad held an impromptu street party to celebrate their Copa del Rey win, the news agency EFE reported on Wednesday.

Athletic won their first major trophy in 40 years when they lifted the Copa in Seville on Saturday, beating Mallorca in a penalty shootout when the final finished 1-1 after extra time.

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The club’s official celebrations are due to take place on Thursday, when — following Athletic Club tradition — the barge ‘La Gabarra’ will carry the squad and trophy along the river Nervion, through the centre of Bilbao, accompanied by a flotilla of smaller boats.

However the squad held a spontaneous, unplanned celebration on Tuesday, accompanied by music from a ‘txaranga’ or amateur band, led by forward Asier Villalibre, who plays the trumpet.

Videos on social media showed a number of players partying on the street — including captain Iker Muniain and forward Iñaki Williams, who broadcast the celebrations live on Instagram — who were soon joined by hundreds of fans.

Athletic Club released one video on its social media channels, showing Muniain addressing the crowd and singing.

“You’re not going home yet, are you?” Muniain said. “We’ll stay here a little bit longer. It was really hard, a lot of pressure, 40 years waiting for this moment.

“That’s why the players wanted to be here today with the people, in the city. When we say this is a family, they aren’t empty words.”

“What was that about yesterday? We’re crazy!” Iñaki Williams posted on X. “I don’t know what it will be like on Thursday, but yesterday was one of the best days of my life.”

EFE reported that the Ertzaintza, or Basque police, had opened an inquiry over a public gathering without notifying the authorities, which can result in an “adminstrative penalty” such as a fine, for a breach of public safety laws.

The names of the four players being investigated have not been released.