The Brazilian-born Costa said that his future is at Chelsea, reports EFE. Costa's remarks came after the defending champions' 0-2 defeat by Chile in the World Cup group stage, leading the Spaniards' shocking, early exit from the championship.
The Spaniard called Atletico his "home", where his heart is, but "life goes on, and we should accept that".
Costa didn't disclose a lot of information about the deal, since he was focused on the World Cup.
"I've always wanted to play in the Premier League and Chelsea is one of the best teams in the world, so there were a lot of reasons that led me to make my decision," Costa said.
"Each season is different but none is easy. I'm going to have to work hard to adapt to the style of the Premier League," he added, according to telegraph.co.uk.
"Why did I choose to sign for Chelsea? It's going to happen. It's all about taking my career in the right direction. If all goes well, that's where I'll be next season."