The 26-year-old winger, born in Barcelona, has signed a five-year contract that ties him to Espanyol until 2031. The club's sporting management reached an agreement with Castellón after what new sporting director Monchi described as very positive negotiations.
Espanyol triggered a release clause worth more than €5 million, which will be paid in instalments, with the agreement also including a buy-back option and a 15 per cent sell-on clause in Castellón's favour.
Calatrava arrives to strengthen Manolo González's attack. His season with Castellón was more than notable, with the club falling just short of promotion after losing to Almería in the play-off semi-finals, while he produced excellent numbers.
In the Segunda División, Calatrava made 75 appearances across his two seasons at the club, scoring 21 goals and providing 19 assists, with 15 of those goals coming in his final campaign alone in all competitions.
The winger came through Catalan football, playing for Horta, Sant Andreu, Sants and Costa Brava before joining Atletico Madrid's academy, where he helped the club's reserve side win promotion to Primera Federación. He later moved to Castellón as a free agent in the summer of 2024, going on to become one of the Segunda División's most in-demand players.
Calatrava's arrival represents Espanyol's first reinforcement of the summer and Monchi's first operation since taking over the club's sporting department. The signing adds an important attacking option, bringing quality, unpredictability, talent and a determination to deliver end product in the final third, a profile Manolo González had reportedly wanted for several seasons.
Calatrava will be presented next Tuesday at the RCDE Stadium, where he will face the media for the first time as an Espanyol player and undergo medical tests along with the rest of the squad.
Espanyol are expected to continue their business in the coming hours. Left-back Hartman, who played for Burnley in England last season, could become the club's second signing of the summer following Calatrava's arrival.
The move brings Calatrava back to his home city having left Barcelona's grassroots system as a teenager, completing his development in Atlético Madrid's academy before making his name in Segunda División with Castellón.