The Champions League final between Chelsea and Manchester City will be played at Porto's Estadio do Dragao on May 29, UEFA has confirmed.
UEFA had wanted to move the final to Wembley and was in talks with the UK Government, but there was a considerable sticking point over waiving quarantine rules for the 2,000 staff, sponsors, VIPs and foreign media.
The fixture was due to take place at the Ataturk Stadium in Istanbul, but pressure mounted for the venue to be changed after the UK government placed Turkey on its 'red' list of at-risk countries and urged fans not to travel for the fixture.
UK citizens returning from red-list countries are required to quarantine at a government-approved hotel for 10 days.
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How many fans can attend - and will they have to quarantine?
UEFA has confirmed 6,000 City and Chelsea fans will be allowed to attend although the overall stadium capacity is still to be finalised.
Portugal is on the government green list so UK visitors will be able to travel there from Monday May 17, as confirmed by Portugal's foreign minister on Friday. They will not need to quarantine but they will have to take Covid-19 tests before and after they travel.
Portuguese Minister of State Mariana Vieira da Silva expects all supporters will come in a bubble and have no contact with the general population.
Fans must come and go with charter flights on the same day and shall be taken straight to the stadium and back after the final.
Chelsea said in a statement on Friday: "Chelsea Football Club is currently working with UEFA on arrangements for supporters attending the Champions League final against Manchester City on Saturday 29 May.
"We will communicate information as soon as it is available and thank our supporters for their patience.
"It was announced yesterday (Thursday) that the final will now take place at Porto's Estadio do Dragao in northern Portugal, after Covid restrictions meant supporters would not be able to attend the match at its original venue in Turkey."
Speaking at a press conference after a Council of Ministers meeting, Vieira da Silva said the final would have a limit of 12,000 fans at the stadium.
Explaining the move, UEFA said in a statement: "After a year of fans being locked out of stadiums, UEFA thought that everything needed to be done to ensure the supporters of the two finalist teams could attend.
"UEFA discussed moving the match to England but, despite exhaustive efforts on the part of the Football Association and the authorities, it was not possible to achieve the necessary exemptions from UK quarantine arrangements.
"The Portuguese authorities and the FPF stepped in and worked quickly and seamlessly with UEFA to offer a fitting venue for the final and, as Portugal is a green list destination for England, fans and players attending the final will not have to quarantine on their return home.
"The decision does not come without big regret for the work that the Turkish football authorities have done over the last two years to ensure the successful staging of the final in Istanbul. UEFA is grateful also for their continued partnership and cooperative spirit as well as the understanding they showed in this particular circumstance and will urgently look into future opportunities for the city of Istanbul."
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This will be the third final in Portugal in eight years but the first in Porto.
UEFA President Aleksander Ceferin said: "I think we can all agree that we hope never to experience a year like the one we have just endured.
"Fans have had to suffer more than twelve months without the ability to see their teams live and reaching a Champions League final is the pinnacle of club football.
"To deprive those supporters of the chance to see the match in person was not an option and I am delighted that this compromise has been found.
"After the year that fans have endured, it is not right that they don't have the chance to watch their teams in the biggest game of the season.
"Once again we have turned to our friends in Portugal to help both UEFA and the Champions League and I am, as always, very grateful to the FPF and the Portuguese Government for agreeing to stage the match at such short notice."
Ceferin's statement continued: "The Turkish football federation and the Turkish authorities have recognised the UEFA's efforts to give fans of the competing clubs a chance to watch the game. The Turkish Football Federation and the authorities have always been reliable partners of UEFA and Turkey has hosted many UEFA events over the years with great success. I hope to be in Istanbul and Turkey for a Champions League final and many other events in the near future.
"I hope the final will be a symbol of hope at the re-emergence of Europe from a difficult period and that the fans who travel to the game will once again be able to lend their voices to showcase this final as the best in club football."
Why Wembley proposal fell through
Analysis from Sky Sports News reporter Kaveh Solhekol:
The Champions League final is not being held at Wembley because UEFA could not receive the assurances it required from the UK government that anyone who had a ticket or was working at the game would be able to attend without needing to quarantine.
UEFA believes it has received those assurances from the Portuguese government for the final to be held in Porto on May 29.
It has also received the same assurances from the Polish government for the Europa League final between Manchester United and Villarreal in Gdansk on May 26.
If UEFA cared only about sponsors and VIPs it would have kept the final in Istanbul. The final is being moved so Chelsea and City fans can attend. UEFA operates on the principle that general public fans should also always be able to attend the final.
There are significant costs involved with moving the final at such short notice but UEFA feels it is the right thing to do so fans can attend.
The costs would have been much higher if the game had been at Wembley and UEFA had been unable to fulfill its contractual obligations to its broadcast partners and sponsors.
As far as UEFA is concerned, without broadcast partners and sponsors there would be no Champions League.
Some 97 per cent of the revenue generated by commercial and broadcast deals is redistributed to the clubs who play in the Champions League.