The attacking midfielder was a target for Liverpool last season but the deal fell through after the player failed a medical and the French club decided to sell him to Betis after he entered the final year of his contract.
The deal for the 26-year-old Frenchman includes up to an additional 10 million euros in add-ons and Lyon will also receive a 20% sell-on fee if he leaves Betis.
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"Olympique Lyonnais thanks Nabil for all he has brought to the club, for his professionalism and especially for his involvement in the professional group as team captain.
" Fekir's younger brother Yassin, 22, has also moved to Betis, with Lyon to receive 50% of any future transfer fee for the striker if he leaves the La Liga side.
Nabil Fekir scored 69 goals in nearly 200 matches with Lyon, becoming club captain in 2017 before winning the World Cup with France last year.
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