In the wake of Prime Minister Theresa May triggering Article 50 some of the leaders of the 27 remaining EU states have mourned the split between Britain and the bloc.
Meanwhile, papers across the globe featured the landmark moment on front pages.
Germany's Die Welt merely said: "Farewell".
While, France's Liberation added: "We miss you already."
Sweden's Prime Minister Stefan Lofven said it regretted the UK's decision, describing it as a "close and valuable partner in the EU".
He said he welcomed "the constructive approach" in Theresa May's letter and hoped the relationship between the two countries would be "as positive and mutually beneficial as possible even after withdrawal".
German Chancellor Angela Merkel said she wants Britain and the EU to be "close partners" and said member nations will conduct negotiations in a "fair and constructive manner".
Die Welt puts out a Mayday distress signal as Britannia seeks to rule the waves with an e.e. of 3.6 per cent in her sails. pic.twitter.com/tIWS4FRggu— Fraser Stoddart (@sirfrasersays) March 29, 2017
She added: "I hope that the British government will also approach the talks in this spirit."
Mark Rutte, Prime Minister of the Netherlands, said his country had a long history with the UK, which is one of its main trading partners.
He said it was important "the best possible" relationship was established between the EU and Britain.
Maltese Prime Minister Joseph Muscat described it as "a sad day for Europe".
He said: "Nobody can rejoice about what happened today. There are consequences for everyone; the bloc will work to find a way to mitigate these consequences."
Spain's President Mariano Rajoy Brey tweeted: "The UK has officially communicated its intention to leave the EU. We are prepared. Calm, tranquillity and confidence."
He added: "We will preserve the unity of the 27 state members as we move forward with European integration. Europe is our present and our future."
Unlike the Italian press, El Pais has Brexit front and centre pic.twitter.com/u28j65kUFV— Patrick Atack (@patricvk) March 29, 2017
Portuguese President Marcelo Rebelo de Sousa said in a statement that Britain was its "oldest ally" and "will continue to be a European country".
The Government of Ireland said there was "no doubt" future negotiations would be "challenging".
It added: "Ireland is well prepared for the challenges ahead. We will negotiate from a position of strength as an integral part of the EU 27 team, and will work with all our partners to achieve the best possible outcome."
Belgium's Prime Minister Charles Michel tweeted that its government "will play a constructive and active role in creating a new relationship between UK & EU", adding: "We will defend the European values."
He said: "In the future relationship between the EU and the UK, we want trade relations to be as favourable as possible, and we want effective co-operation to continue in other areas, including security."