The 28-year-old defender joined the Dons in January 2025 and made 56 appearances in all competitions, scoring one goal.
Advertisement
Advertisement
The Dane lifted the Scottish Cup with Aberdeen in 2025 as they defeated Celtic on penalties, Aberdeen's first Scottish Cup triumph in 35 years.
In a statement, Aberdeen manager Stephen Robinson said: "We received a good offer from Elfsborg for Alex and it's one we all felt was right.
"Alex is a great lad who always gave his best for the Club, but I was honest with him in saying that he probably wouldn't be an automatic starter next season."
Robinson continued: "He leaves with a Scottish Cup winner's medal and the thanks of everyone at Pittodrie and Cormack Park. We wish him every success back in Sweden."