"The Omnium family is getting bigger and bigger, and from today, we have the honour to count on the support of actor Viggo Mortensen as a new member," the group said on Twitter in a post re-tweeted by an account of the actor.
La família d'@omnium cada dia és més gran i, des d'avui, tenim l'honor de comptar amb el suport de l'actor Viggo Mortensen com a nou soci. Gràcies per ser-hi, Viggo! 🙌— Òmnium Cultural (@omnium) May 10, 2018
Avui ja som 115.000 socis! Si encara no ho ets, suma-t'hi ➡️ https://t.co/C6nNXCayD6 pic.twitter.com/WBytEJZ60S
The 59-year-old, who grew up in Argentina and currently lives in Madrid, is in a relationship with Catalan actress Ariadna Gil.
Last year, he came out in favour of an independence referendum in Catalonia, which took place on October 1 despite a court ban.
Founded in 1961 to promote the Catalan language and culture that were then being severely repressed by dictator Francisco Franco, Omnium has in the past years become a major actor in the region's secession movement, organising huge protests along with the ANC, another pro-independence group.
Its current president, Jordi Cuixart, has been in jail since mid-October, accused of rebellion for his role in the region's failed secession bid.