Mikel Landa is to leave Team Sky at the end of the season and join Movistar.
Landa impressed at the Tour de France, proving pivotal in helping Chris Froome win the yellow jersey for the fourth time.
The Spaniard finished fourth in the general classification, but is said to have been dissatisfied with Sky's apparent reluctance to allow him to challenge Froome for the title.
And he has now signed for Movistar on a two-year deal.
"It's great news for us," said Movistar general manager Eusebio Unzue. "Being still a young rider and with everything that's he's shown, he should be the rider who leads Spanish cycling for the next few years."
Landa has four Grand Tour stage wins in his career, three of them coming at the Giro d'Italia, where he claimed the King of the Mountains jersey in 2017.