Spanish international Benat Etxebarria has re-joined Athletic Bilbao from Real Betis on a five-year deal, Athletic confirmed.
Spanish media reported that the transfer fee will be around €8m ($10.5m USD, £6.8m).
The midfielder had come through the youth ranks at Athletic, but made just one appearance in the senior team before making the move to Betis in 2009.
He broke into the first team a season later and was a key figure as the Seville side were promoted back to La Liga in the 2010/11 season.
Even better things were to come from the 26-year-old in his first full season in the top flight last year.
His excellent range of passing and delivery from dead-ball situations saw him earn a first call-up to the Spain squad in May 2012, although he eventually just missed out on a place in the world champions' squad for UEFA Euro 2012 in Poland and Ukraine.
This season he made 34 league appearances and scored four goals as Betis finished seventh to qualify for Europe for the first time in eight years.
Athletic meanwhile suffered a disappointing campaign after reaching two cup finals last year as they finished 12th.
The Basque side have been in need of midfield reinforcements since Javi Martinez joined Bayern Munich for €40m back in August.