The 27-year-old Spanish under-21 international – who won the European U21 Championship with his country in 2019 – spent last season on loan at the Andalucian club, where he made 26 appearances.
The La Liga outfit had the option of extending Roca’s loan by a further season or purchasing the player permanently at a knock-down price – with Leeds remaining in the second tier for a second season.
Betis opted for the latter, with reports in Spain suggesting that the final fee is under 5 million Euros.
Roca joined in the summer of 2022 from Bundesliga giants Bayern Munich in a £10m deal.
He featured 36 times in all competitions in a mixed 2022-23 campaign which ended in United being relegated from the Premier League.
Betis exercised Roca’s relegation release clause last summer.
Roca was two years into a four-year deal at Elland Road.
Sheffield Wednesday have sealed the signing of Swedish international attacking midfielder Svante Ingelsson – who has joined from German side Hansa Rostock to become their fourth addition of the summer window.
The 26-year-old follows on from the signings of Max Lowe, Ben Hamer and Yan Valery.
Ingelsson began his career at hometown club Kalmar FF in September 2015 and moved to Italy to join Serie A side Udinese in 2017.
He had a loan spell with Pescara before briefly returning to Kalmar in early 2020 before moving to 2.Bundesliga outfit Rostock in the summer of 2021.
The Swede played 87 games in total for Rostock and has represented Sweden from under-16 to under-21 level.
Middlesbrough have completed the signing of USA international midfielder Aidan Morris.
The 22-year-old, capped five times, has joined the club from MLS side Columbus Crew.
The deal is said to be worth just over £3m with a sell-on clause.
Manager Michael Carrick said: “We’re delighted to welcome Aidan to the club. He’s a good player.
“He suits our style of play, he’s strong, he likes to get on the ball, and he plays off both feet.”
Meanwhile, Boro are set to allow winger Sammy Silvera to join Championship rivals Portsmouth on loan for the 2024-25 campaign.
