Wales beat Russia 3-0 to top their Euro 2016 group - while England are also through to the last 16.
Chris Coleman's men outplayed the Russians in Toulouse, while Roy Hodgson's men could only manage a 0-0 draw against Slovakia in Saint-Etienne.
The Welsh gained six points from their three games after defeating Slovakia in their first match in Bordeaux, while the Three Lions came second with five points after drawing against Russia and beating rivals Wales 2-1.
Group toppers Wales will be off to the Parc des Princes in Paris to play the third place team from either Group A, C or D on Saturday June 25.
The English will now travel on to Nice to play the runner-up in Group F - which features Austria, Hungary, Iceland and Portugal - on Monday, June 27.
Welsh fans were in fine voice at the fan zone in Toulouse, chanting "We are top of the league" as phones were checked for the latest updates from Saint-Etienne.
At the final whistle, arms and beers were thrown aloft in celebration of a well-earned win.
Thomas Roberts, 21, from Bala, said: "This is the happiest day of my life. Seriously.
"What a night. It's just been incredible and we're off to Paris."
Mark Bleasdale, 47, said: "It's been an incredible night, the atmosphere here had been incredible.
"The only thing which could have improved it would be having had a ticket."
England consigned themselves to second place in the group and a trip to Nice after failing to find the net against Slovakia.
Under grey skies with the occasional spot of rain, the hundreds of supporters in the fanzone drifted off into the night feeling rather underwhelmed.
Dean Fitzjohn, from Kent, said: "How can you not beat Slovakia?
"I know a lot of games at this level are tight but we have to be beating them.
"We had so many chances and we have to take them, we're brilliant all over the pitch until we get to the final third."
Those supporters who are staying in France will now have to wait a week before England play again.
Wales fans in Toulouse said they would be celebrating long into the night after their success.
Tom Allen, 23, of Swansea, said: "I said at the start, just doing ourselves justice in the group stage would be enough.
"We've loved being here and to top the group, well, I'm not sure I could say I was expecting that.
"It's been an amazing two weeks so far and if we keep on playing like that, well, who knows how far we'll get?
"At least another round. At least that."
Rhys Evans, 24, also of Swansea, said: "We've just got this belief that's hard to explain. We're fearless and the support has been amazing to see.
"We could have crumbled after the England game but we've come back and demolished Russia. I'm going to wake up not believing what I saw."