Goalkeeper Robert Sanchez will join Chelsea on undisclosed terms.
The switch to West London ends a ten-year association with Albion, in which Rob graduated through the club's academy and age group teams.
Head coach Roberto De Zerbi said, “I’m sorry for the last period. Robert is a good guy and a really good player, but being a coach sometimes means making difficult and painful decisions for the team. I wish him good luck for the future.”
Technical director David Weir added, “This is a good move for all parties. It also gives Rob the opportunity to play and a long-term stability.
“For the club it’s an area in which we have fantastic competition, and this is another significant transfer fee for our academy. It’s credit to all those at the club who have overseen Rob’s progression.
“We would like to thank Rob for his time here and wish him all the very best for the future.”
Rob signed his first professional contract with Albion in June 2015 after joining the club two years prior from La Liga side Levante.
He got his first taste of senior football when he went on loan to Forest Green Rovers for the 2018/19 campaign. He played 17 times for the Gloucestershire club, who reached the Sky Bet League Two play-offs.
Rob spent the 2019/20 season on loan with League One outfit Rochdale, featuring 35 times in league, Emirates FA Cup and Carabao Cup matches, before the season was curtailed due to the Covid-19 lockdown.
He made his Premier League debut for Albion in a 2-1 defeat at Tottenham in November 2020 and his form was rewarded with a new contract in February 2021.
Having become Albion's first choice goalkeeper in December of that year, he received his first call-up to the Spain senior squad in March 2021, before being named in his country's Euro 2020 squad.
He made his international debut in September 2021, coming on as a substitute in a 4-0 win over Georgia.
In total he made 90 senior appearances for Albion, 87 of those in the Premier League.