In a first for BlueCo, Alonso will be the manager rather than the head coach in West London, giving him more control behind the scenes, including transfer decisions.
The Spaniard will begin his role at Chelsea on July 1, leaving Calum McFarlane in charge for the final two Premier League matches, and he's now addressed the supporters with a message after joining.
"Chelsea is one of the biggest clubs in world football and it fills me with immense pride to become manager of this great club," Alonso said.
"From my conversations with the ownership group and sporting leadership, it is clear we share the same ambition. We want to build a team capable of competing consistently at the highest level and fighting for trophies.
"There is great talent in the squad and huge potential at this football club and it will be my great honour to lead it. Now the focus is on hard work, building the right culture and winning trophies."
Clearly excited about his next challenge, Chelsea fans be delighted they've landed arguably the best manager on the market, with the 44-year-old potentially bringing a winning mentality back to the club.