Cristiano Ronaldo.
"Dismayed by the news arriving from Barcelona. Full support and solidarity with the family and friends of the victims," Ronaldo said in a translated tweet from Portugese.
Ronaldo is from Portugal, which neighbors Spain. The soccer superstar also plays professionally for Real Madrid in Spain's top pro league, La Liga.
Rafael Nadal added: "Shattered by what has happened in Barcelona! All my support to affected families and the city," in a translated tweet from Spanish.
Pau Gasol -- who's from Barcelona -- also tweeted, "Sad and horrified by the tragic events that took place today at the #Ramblas of #Barcelona.