By SABC Sport
11th January 2023
The 29-year-old has joined for a reported £13million subject to international clearance and a visa application.
He becomes the first signing under Unai Emery, who had targeted a wideman in the January transfer window.
Emery told the club's official site: "Alex is a good player that can help our squad. He has been one of the top left-backs in LaLiga over the past few seasons and we are delighted to have him here."
Moreno can operate on the left side of midfield and also adds competition for Lucas Digne, who only arrived from Everton for £25million last year.
He made 122 appearances for Betis, scoring six times, after moving from Real Vallecano having started his career at Mallorca.