A late goal from Daniel Sturridge was enough to help England beat Wales 2-1 in Lens on Thursday and break Welsh hearts.
Wales now lie in second place in the group, one point behind England and ahead of Slovakia thanks to a superior head-to-head record.
So, what does that mean for Wales' chances of qualification from the group?
It means a win against Russia would be enough to see Wales safely through to the next stage of the competition, without worrying about third-place scenarios.
On top of that, if England were to fail to beat Slovakia in their final fixture, then a win for Chris Coleman's side on Monday would see them qualify as group winners.
But, what about the other scenarios?
Remember, if teams are tied on the same number of points in the group, the head-to-head result between the two sides is the first criteria to see who finishes ahead of who.
If Wales draw with Russia
In this scenario, if England were to win against Slovakia, that would see Wales qualify in second place, two points ahead of Jan Kozak's side.
However, if the Slovaks were to beat the Three Lions on Monday, that would leave Wales in third place and in the hands of UEFA's new system for this year's tournament.
Remember, the four best third-placed teams qualify for the last 16, with the first criteria points gained, followed by goal difference.
If there was a draw between Slovakia and England - then Wales go through as runners-up as they would be level on points with Slovakia but won the head-to-head between the two sides.
If Wales lose to Russia
Let's hope it doesn't come to this.
In the event of a Wales loss, any result for Slovakia against England would see Wales knocked out of the competition.
However, if England were to beat Slovakia, then Wales could still have a reprieve - if they ended up as one of the four best third-placed teams out of all the Euro 2016 groups.
Again, to reiterate, the best third-placed teams will be decided on points gained followed by goal difference.In conclusion, we need to win at eight o'clock on Monday evening. I imagine I will be watching it at home (ITV 4: Freeview channel 24). It's not likely to get much of a look in in South London's honky tonks and dive bars with an equally vital England game on at the same time.