Alonso is known for his performances on television in
Rías Baixas (2003–2005),
Maridos e mulleres (2006–2008),
Padre Casares (2008–2015), and
Gondar (2009) at a local level in
Galicia and nationally for playing characters such as Diego Murquía / Adrián Vera Celande in historical drama
Gran Hotel. He played the role of
Andrés "Berlin" de Fonollosa in the
crime drama series
Money Heist (
La casa de papel), which aired on
Antena 3 in 2017 and was later broadcast on
Netflix. In 2018, he was chosen as "International Star of the Year" by
GQ Turkey magazine. He co-starred in
Diablo Guardián,
Amazon Prime Video’s first drama series in
Latin America, which was released in May, 2018. In 2019, Alonso played the leading role in the mystery thriller
The Silence of the Marsh. He reprised his role of Berlin in a
spin-off series of the
same name, which premiered in 2023. == Personal life ==