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Williams decided to commit to the Bilbao club for a further eight years, and his release clause, which was reported to be around €58 million ($104.3 million), has also been increased by 50 per cent as part of his new contract, the club announced.

It looked like Williams was set to join Barcelona, whose sporting director, Deco, had confirmed its interest, although Athletic questioned if the Blaugrana would be able to afford the transfer, given Barca's financial problems.

After the transfer fell through, Williams penned a new contract to run until 2035, an eight-year extension on his previous deal, which was due to expire in 2027.

"I think we have a very long season ahead of us," Williams said. "We have very ambitious titles like the Champions League, which everyone would like to play in.

"What could be better than doing it with the club of my life? I would like to continue making history here at San Mames, with the fans, with my family, and with a lot of enthusiasm."

Williams's decision to stay means he will continue playing alongside his brother, Inaki, who will captain Athletic this season.

"We've both always dreamed of this moment," Williams added. "My brother is a role model for everyone, especially for me.

"I think he's the best person to be captain, and I can't wait to see him wearing the armband for a long time."

Athletic Club will begin its 2025-2026 campaign at home against Sevilla on 18 August (AEST).