Giovani Lo Celso will spend the 2019/20 season with Tottenham.
The north London club's pursuit of the Argentina international had been widely reported throughout the summer, and the club finally got its man on the final day of the Premier League transfer window.
Tottenham announced the signing via a statement on the club's website.
"We have reached agreement for the season-long loan signing of Giovani Lo Celso from Real Betis Balompié with an option to make the transfer permanent.
"The attacking midfielder will wear the number 18 shirt this season."
Lo Celso originally joined Betis on loan from PSG, but the LaLiga side made the deal permanent in April with a $25 million purchase option.
But the arrival of Nabil Fekir to the Seville club last month was viewed by many as a strong indicator fellow midfield left-footer Lo Celso would join Tottenham.
The chance to work with compatriot Mauricio Pochettino in London was reportedly a huge selling point for the 23-year-old who impressed during his first full season with Betis.