Has Brexit now happened and has the UK left the European Union?
No. The UK is still a full member of the EU. What has happened with Theresa May signing a letter to the European Council is that the formal two-year process of leaving the EU has started. There will now be months of negotiations to agree terms, and the final deal will be voted on by the UK and European Parliaments for ratification.
How did the Australian Prime Minister Malcolm Turnbull mock Donald Trump, comments which were recorded now released to the media?