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Get ready for a big Brexit moment this week.

Members of Parliament (MPs) are going to vote for what could be the final time on whether to support or block Theresa May's Brexit deal on Tuesday.

This is the agreement that the prime minister negotiated for the UK's exit from the European Union.

There are just weeks to go until the UK is due to leave the EU on Friday 29 March.

But depending on what happens this week, there's still time for a last minute twist.

Read our guide below and don't forget to try our interactive explainer to see what could happen next with Brexit.

Why are MPs voting again on the Brexit deal?

MPs have already voted once before on Theresa May's Brexit deal.

In January, 432 MPs voted against the deal, while 202 voted to support it. It was the biggest defeat a government has faced in almost 100 years.

The main reason MPs voted against it last time round was because of the Irish backstop.

This is the part which aims to keep an open border between Northern Ireland and the Republic of Ireland if the UK and the EU can't agree a long term trading relationship.

The government's been trying to get the EU to make changes to the backstop to win over MPs so that this time they'll vote for the deal.

On Monday night following last minute talks with the EU in France, Theresa May said "legally binding" promises had been on this issue.

The prime minister said the changes meant the Irish backstop could not "become permanent".

She called on MPs to now "come together" to vote for her Brexit deal in Parliament.

What is happening on Tuesday?

Theresa May's deal is expected to face a "meaningful vote" in Parliament on Tuesday.

We won't know the exact time until the government announces it.

If Mrs May's deal is approved by MPs, her plan for leaving the EU will go ahead.

The agreement has already been approved by other EU leaders.

What happens if the deal is rejected again?

If politicians vote AGAINST the prime minister's deal on Tuesday, then there'll be another vote.... but a different question.

This vote will happen on Wednesday and will ask whether the UK should leave without a deal.

If MPs say they don't want to leave without a deal, MPs will get a third vote on Thursday on whether to request a delay to Brexit from the EU.

If they voted yes to this then politicians would be given more time to decide what to do next. It's expected that would only be a short break though - probably about three months.

The EU would have to agree to that and the big issues, which have been holding things up so far, would still be there.

The Labour Party says it would back the idea of a new referendum altogether.

But it's decision time, and depending on how these votes go the UK could be leaving the EU at the end of March on schedule - or not!