Former British Prime Minister Tony Blair | Charles McQuillan/Getty Images Tony Blair: Brexit is not a ‘foregone conclusion’ Former British prime minister warns of ‘Brexit fatigue.’

Britain's exit from the European Union is "by no means a foregone conclusion," former British Prime Minister Tony Blair told German newspaper Die Welt in an interview published Thursday.

The former Labour Party leader urged Europe to be open to the possibility that Britain could change its mind about leaving the bloc, and warned against "Brexit fatigue" and a "dangerous fatalism" emerging across Europe.

"There is a lack of understanding of how harmful Brexit is for Europe too," Blair told the German paper, adding that Europeans should negotiate "openly" in case "Britons change their minds" about Brexit.

Blair's comments reiterate a statement published via the Tony Blair Institute for Global Change, a think tank, on Thursday in which he argued British citizens have the right to "rethink the decision," now that the potential impact of Brexit is clearer than it was ahead of the vote in June 2016.

Blair also warned that, once outside the bloc, the U.K. would inevitably seek to justify its departure and encourage other EU members to follow suit.

"When there are tensions between EU members, [Britain] will behave differently than it did when it was a member. This will not be good for Europe," he said.

"The fears that motivated Britain to vote for Brexit are not limited to the U.K.," he also said. "That's why it would be prudent to negotiate rationally and with stronger leadership; to use Brexit to deal with the root causes of these fears, which are just as prevalent on the Continent ... If we don't address these, populism will only keep growing."