Paris Saint-Germain and Manchester City, two of the leading candidates to win the Champions League, will face each other in the group stage of this season's competition after coming out together in Thursday's draw.
Pep Guardiola's City beat PSG in the semi-finals of last season's Champions League on the way to losing the final to Chelsea in Porto.
Qatar-owned Paris responded to that disappointment by signing Lionel Messi and there is a chance that the two meetings of the clubs could see the Argentine come up against his great rival Cristiano Ronaldo.
The Portuguese forward is being strongly linked with a move to Abu Dhabi-owned City from Juventus before the European transfer window closes on Tuesday, August 31.
"It is special, Manchester City are one of the best teams in Europe and have been fighting to win the Champions League for 10 years," said PSG coach Mauricio Pochettino.
"The challenge is to try to finish first in the group."
The clubs are in Group A along with RB Leipzig and Belgian champions Club Brugge.
Leipzig were already in a group with PSG last season, the two sides qualifying for the last 16 ahead of Manchester United.
The Germans, who also lost to PSG in the 2020 semi-finals, lost coach Julian Nagelsmann to Bayern Munich in the summer and replaced him with the American Jesse Marsch.
Holders Chelsea will play Juventus in Group H and both clubs will be expected to advance from a section also including Russian champions Zenit Saint Petersburg and Malmo.
The Swedish champions knocked out Steven Gerrard's Rangers in the third qualifying round.
Saint Petersburg will host this season's Champions League final on May 28 next year.
Thursday's draw in Istanbul also saw Barcelona come out in a fascinating Group E along with Bayern, Benfica and Ukrainian champions Dynamo Kiev.
For Barca it will be a first meeting with Bayern since they were humbled 8-2 by the German giants in Benfica's Estadio da Luz in Lisbon in the quarter-finals a year ago.
Ronald Koeman's side are embarking on a first Champions League campaign since the departure of Messi, with whom they last lifted the trophy in 2015.
"Barcelona is a different team without Messi, but they still have good players in their ranks. We want to get through the group, ideally as winners," said Bayern sporting director Hasan Salihamidzic.
Liverpool will face Spanish champions Atletico Madrid, meaning a return to the Wanda Metropolitano stadium where they beat Tottenham Hostpur in the 2019 final to win the European Cup for the sixth time.
Jurgen Klopp's side will also play AC Milan and FC Porto in Group B. Milan, the seven-time winners of the trophy, are back in the Champions League for the first time since 2013/14 after coming second in Serie A last season.
"I laughed, to be honest, pretty loud because it is a tough group obviously," Klopp told Liverpoolfc.com.
Manchester United came out in Group F with Villarreal, Atalanta and Swiss champions Young Boys.
Ole Gunnar Solskjaer's side lost to Villarreal on penalties in last season's Europa League final.
Real Madrid, the record 13-time European champions, are in the same group as Italian champions Inter Milan and Shakhtar Donetsk of Ukraine for the second straight season.
Debutants Sheriff Tiraspol of Moldova complete Group D. They have come through four qualifying ties to reach the group stage, notably knocking out Red Star Belgrade and Dinamo Zagreb.
Erling Haaland's Borussia Dortmund will play fellow former winners Ajax as well as Sporting Lisbon and Besiktas in Group C, while Lille, Sevilla, Red Bull Salzburg and Wolfsburg make up Group G.
The first round of fixtures will be played on September 14 and 15.
It remains to be seen if UEFA will lift its blanket ban on away fans attending matches in European competition.
Pressure group Football Supporters Europe this week called for UEFA to reconsider, saying "guidelines on away fans should be decided on a case-by-case basis in line with the local public health situation".
UEFA will release a fixture schedule for the group stage in due course. The final group fixtures will be played on December 7 and 8.