Perez announced via his social media channels on Wednesday that he would be leaving Racing Point at the end of the Formula 1 season after seven years with the Silverstone-based team.
Racing Point confirmed on Thursday morning that four-time world champion Sebastian Vettel would be joining in Perez's place for next season, when it will be rebranded as Aston Martin.
Perez did hold a valid contract for 2021 with Racing Point after signing a three-year deal last season, and felt secure of his future with the team last month.
But Perez revealed that it was only on Wednesday that he received confirmation from Racing Point that he would be leaving, during a phone call from team owner Lawrence Stroll, who said the team was going in "another direction".
"Nobody told me anything, but I already knew and figured out a couple of things," Perez said. "Final confirmation came yesterday.
"It's fine. Seven years with the team, I know everything has a beginning and also an end. We still have nine races to make each other proud."
Perez said as recently as the Spanish Grand Prix that it was a "matter of time" until speculation linking Vettel with his seat disappeared, as he was receiving feedback from the team that he would remain for 2021.
"That was the feedback that I was getting, that the team wanted to keep me and so on," Perez said on Thursday.
"There were some discussions in the background about contracts and so on, that I'm not willing to disclose because I think those things should remain between the team and myself.
"There were a couple of things in the contract that we went through. In the end, they officially told me yesterday that I'm not continuing.
"I didn't expect that. It is how it is."
In announcing his Racing Point exit, Perez stated that he had no plan B in place as he did not expect to be leaving the team.
While he did not wish to say he felt disappointed by how Racing Point handled the decision, Perez said greater clarity would have helped him plan for his future better.
"I understand it, it's the negotiations going on. They probably took longer than I thought," Perez said.
"Probably a bit more clarity would have helped regarding my future as well. Then I would have looked for a plan B, which probably wouldn't have changed anything."
Asked by Motorsport.com what his next step would be, Perez said his priority was to remain in F1 so long as he can find a competitive package.
"I think everything is an option right now," Perez said. "My main target is to remain in F1. I feel that I'm still very young and hungry, and want to carry on in Formula 1.
"But it has to be the right package. A package that really gives me the maximum motivation to give my 100% every single lap.
"It's also got to be a long-term project, targeting 2022, because there I expect the rule change to play a major effect. That's the main reason that I want to continue for '22, because I feel there are plenty of opportunities.
"I don't expect to make a decision any time soon. I will take the time that I require. If I don't find anything attractive in F1, I would think about other series, other things, we'll see."