A European official described Boris Johnson's No Deal Brexit strategy as a "tragedy" for both the EU and Britain as Mr Johnson swept to victory in the Tory leadership contest.
Deputy head of the European Commission Frans Timmermans said: "A no-deal Brexit, a hard Brexit, would be a tragedy - for all sides, not just for the United Kingdom.
"We are all going to suffer if that happens."
Mr Johnson has repeatedly expressed his intention to either renegotiate the stalled divorce agreement with the bloc or leave without a deal by an Oct 31 deadline.
Mr Timmermans continued: "The United Kingdom reached an agreement with the European Union and the European Union will stick to that agreement.
"We will hear what the new prime minister has to say when he comes to Brussels... This is the best deal possible."
The EU is bracing for a no-deal Brexit, or another delay to Britain's departure should Mr Johnson follow through on his promises as Britain's leader.
Mr Timmermans said the EU would hold the line on Brexit and that Johnson's flamboyant "character or persona or attitude" made no difference.
Prime Minister-in-waiting Mr Johnson defeated rival Jeremy Hunt in a landslide win of 92,153 to 46,656 in the vote of Tory party members.
