Please answer a question about the following article about FC Barcelona:

Like Maradona, Ronaldo only stayed a short time before he left for Internazionale. However, new heroes emerged, such as Luís Figo, Patrick Kluivert, Luis Enrique and Rivaldo, and the team won a Copa del Rey and La Liga double in 1998. In 1999, the club celebrated its centenari, winning the Primera División title, and Rivaldo became the fourth Barcelona player to be awarded European Footballer of the Year. Despite this domestic success, the failure to emulate Real Madrid in the Champions League led to van Gaal and Núñez resigning in 2000.

In what year did Barcelona win the Primera División title?
1999