Boris Johnson's departure as prime minister can lead to a more "constructive" and "respectful" relationship between Britain and the EU, Michel Barnier has said.
The former chief Brexit negotiator, who put together the withdrawal agreement in talks with Mr Johnson's team, said he hoped things could become "more friendly".
The prime minister announced he was stepping down on Thursday afternoon after Cabinet revolt that saw more than 50 Tory MPs walk out of governemnt jobs.
The turmoil has not gone unnoticed across the Channel.
"The departure of Boris Johnson opens a new page in relations with the UK," Mr Barnier said in a message posted on social media.
"May it be more constructive, more respectful of commitments made, in particular regarding peace & stability in NI, and more friendly with partners in the EU.
"Because there’s so much more to be done together."
The former head of the EU's Brexit task force, who has since retired from the European Commission, was perhaps the most recognisable face of the European Union during Brexit talks.
All likely candidates to replace Boris Johnson as prime minister are committed to Brexit, though some like Ben Wallace and Liz Truss supported Remain before the referendum.
But it is the particularly combative approach the UK took to relations with the EU that Mr Johnson took which Brussels will hope might be dialled back.
The prime minister was often accused of using Brexit as a political tool to rally support at home among Tory MP and Leave voters – deliberately causing problems so he could face off against the EU.
It is the prime minister’s approach to the Northern Ireland border that is causing the most anguish in Brussels currently. The prime minister has passed legislation to unilaterally overwrite parts of the deal, which the EU and most observers say breaks international law.
MEPs in the European Parliament slammed Boris Johnson‘s “Fawlty Towers approach to politics” on Wednesday, with parties from across the EU political spectrum gathering in in Strasbourg to slam the UK’s plan to tear up parts of the Brexit deal.
Boris Johnson has characterised the changes as minor, European Commission vice president Maros Sefcovic, who has taken over Mr Barnier’s Brexit duties, said the approach had “no political or legal justification whatsoever”.
He said that it was “legally and politically inconceivable that the UK decides” how the EU’s trade border was enforced, a situation which the legislation would effectively create.
