AMID all the gloom and angst of Brexit, Donald Tusk was able raise a smile when he received a touching note from a six-year-old British schoolgirl.

The letter read: "Dear Mr Tusk, I live in Britain. I know we are leaving the EU. But I think we should be friends. From Sophie, aged 6."

Mr Tusk responded in his social media post by writing: "We will always be friends, Sophie."

But the letter also included a drawing of a unicorn, a term which has been used as slang for the unrealistic plans pursued by some UK lawmakers during the Brexit negotiations.

A European Council spokesman confirmed Mr Tusk had received the letter, adding: "He found it heart-warming and has sent Sophie a signed photo as she asked for."

When one Twitter user accused the letter of being "fake but funny," the EU Council's press account responded directly, reiterating that the photo was "definitely" a letter Mr Tusk had received, describing Sophie as "his friend".

The press team did not confirm whether the unicorn carried additional meaning but noted how social media posts were open to personal interpretation.

Guy Verhofstadt, the European Parliament's Brexit co-ordinator, praised Sophie's letter, tweeting: "Sometimes it takes a child to put everything in perspective."

He added: "What a terrible waste #Brexit is."

Mr Tusk has a history of tongue-in-cheek social media posts on Brexit.

In September, he shared a photo of himself and Theresa May choosing a sweet treat from a spread of food at a summit in Salzburg.

"A piece of cake, perhaps? Sorry, no cherries," the post read, in an apparent reference to cherry-picking in the process of the UK's negotiations with the EU.

In February, the Council President prompted angry responses when he tweeted: "I've been wondering what that special place in hell looks like, for those who promoted #Brexit, without even a sketch of a plan how to carry it out safely."