Brussels, Belgium (CNN) At the end of a dramatic day here in Brussels, Theresa May was thrown what could very well be her last Brexit lifeline.

At 11.20 p.m. local time, Donald Tusk, President of the European Council, finally announced that 27 EU leaders had agreed unanimously on a response to the British Prime Minister's request to delay Brexit and avoid a chaotic split on March 29. And to everyone's surprise, they offered her two options.

First, a short delay, giving the UK until May 22 to get its affairs in order before leaving the EU. But that option is only available if lawmakers in the House of Commons approve May's overall withdrawal deal next week.

Alternatively, option two kicks in if May loses the third "meaningful" vote on her deal. That allows the UK to stay in the EU until April 12, at which point it must make a choice: Take part in the European parliamentary elections in May and seek a longer delay to Brexit, or don't. Should it come to it, the implications of that decision will be the next big Brexit bust-up.

It all seems quite simple. But it's hard to explain how tense things felt in the EU capital on Thursday. As a promised 6 p.m. press conference got pushed back, all that was clear was that nothing was clear at all.

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