Michel Barnier announced on Thursday morning that he has tested positive for Coronavirus.
In a video message on Twitter, 69-year-old Barnier said, "I would like to inform you that I have tested positive for COVID-19. I am doing well and in good spirits. I am following all the necessary instructions, as is my team."
He added, "For all those affected already, and for all those currently in isolation, we will get through this together."
Well wishes immediately flooded in from across Europe - relaying messages of support from both politicians and citizens.
European Commission President Ursula von der Leyen wished Barnier a speedy recovery, adding, "We are wholeheartedly with you. #OneForAll."
Her European Council counterpart Charles Michel said, "Get well soon my dear Michel Barnier. Wishing you a speedy recovery. I am convinced we will win this battle against COVID-19 together. #StrongerTogether."
European Commissioner for Neighbourhood and Enlargement, Oliver Varhelyi, said, "Dear Michel! Wishing you quick recovery and want to see you back soon!"
"I would like to inform you that I have tested positive for COVID-19. I am doing well and in good spirits. I am following all the necessary instructions, as is my team" Michel Barnier, chief EU Brexit negotiator
Polish EPP MEP and member of the European Parliament's Brexit Steering Group, Danuta Hubner, said, "It is thanks to his indefatigable work that the EU put forward its proposal for the negotiations agreement with the UK."
She added, "Thank you, Michel, for you and your team's great efforts. I keep my fingers crossed. Take care, all of you."
Austrian EPP deputy Lukas Mandl said, "I always experienced you as a strong and healthy man. I trust you will fully recover and be back strong. We need you as a great person and also for a good future relationship between EU and UK. Take care!"
Political differences were cast aside in the midst of the escalating Coronavirus crisis, with fervent Brexiteers also sending messages of support.
Former Brexit Party MEP Martin Daubney said, "Get well soon, captain. Wishing you all the best from the UK, despite our obvious differences, this is bigger than politics. Godspeed to you and your all."
"It is thanks to his indefatigable work that the EU put forward its proposal for the negotiations agreement with the UK" Danuta Hubner MEP
Brexit Party colleague Belinda De Lucy echoed the well wishes, tweeting, "Get well soon Michel, hope you recover quickly."
With the EU's chief negotiator now in self-isolation, questions are arising as to the possibility of extending the current Brexit transition period - due to expire on 31 December of this year.
However, UK Prime Minister Boris Johnson has repeatedly ruled out an extension, saying, "There is legislation in place that I have no intention of changing."