It isn't clear when the account was suspended, but Twitter users started noticing the suspension early on Wednesday morning. It wasn't clear that the account was fake until Twitter's communication team explained on Sunday night that it was suspended for "impersonation" based on "a valid report we received from Russian officials."
The last available archive of Putin's English account is from November 18. The account was opened in November 2012. In 2014, Business Insider reported on tweets issued by the fake account as official statements of the Russian president.