Here's the letter of congratulations the EU sent to Donald Trump
Trump overcame all the odds to inflict a shock defeat on experienced Democrat Hillary Clinton and earn his place in the White House.
In the letter, Tusk offers his "sincere congratulations" to the new president on behalf of the European Union and invites Trump to visit Europe to meet up with EU officials as soon as possible.
He adds that he hopes Trump will continue to value the "bridges" between the US and 28-nation bloc, which he says are based on freedom, human rights, democracy, and a belief in the market economy.
Here's the letter:
Some of Tusk's EU colleagues have published reactions to the shock result - not all are congratulatory, though.
Guy Verhofstadt, the former Belgian prime minister who will be the EU Parliament's chief Brexit negotiator, said the US missed a valuable opportunity by choosing Trump over Clinton.
Michel Barnier, another EU politician who will play a key role in Brexit talks, posted the following tweet. Roughly, it translates as: "Like yesterday, I think today that it is better, for the Europeans, being together rather than each at home and every man for himself..."
Trump said he supported Brexit in the run-up to the June referendum and billed himself as "Mr. Brexit" in the run-up to his remarkable victory. Nigel Farage, the UKIP leader who campaigned passionately for Brexit, appeared alongside Trump at a pre-election rally in Mississipi.