Guardiola won 14 major trophies during his tenure at Camp Nou, before leaving in 2012.
While it has been four years since Guardiola left Barcelona, his legacy still remains.
Under Guardiola, Barcelona rewrote the football manual -- his philosophy of "tiki-taka" brought a whole new dimension to the game and changed the way it was played across the world.
His two European triumphs and three domestic league titles came at a time when the team appeared unbeatable.
But both have moved on -- Guardiola at City after winning three straight league titles with Bayern, and Barcelona at its imperious best under current coach Luis Enrique.
This will not be the first time Guardiola has returned to Barcelona -- that came with Bayern Munich in 2015. On that occasion, Barcelona won through to the final after a 5-3 aggregate victory.
City reached the semifinals last season before going down to eventual champion Real Madrid -- and Guardiola has his work cut out if he is to bring the trophy back to England anytime soon.
La Liga to dominate?
There may be 32 teams fighting it out to become Europe's top team but it's difficult to look past the usual suspects.
Spain has provided the winners for the past three seasons -- with two all-Spanish finals in that time.
So how about a repeat this time around? Well that could be a problem for Real -- but perhaps not in the group stages.
Real will face Borussia Dortmund, Sporting and Legia Warsaw -- a trio of clubs which most would expect Madrid to overcome and finish in the top two of Group F.
No team has ever successfully defended the title since the competition was revamped in 1992 -- and there's a few who are determined to make sure Real doesn't make it.
First up in terms of rivals is Barcelona -- the Spanish champion and one of the outstanding favorites.
In Lionel Messi, Luis Suarez and Brazil star Neymar, Barca has a front three to give defenders nightmares.
The trio was on fire last season, leading Barca to the league and cup double as well as the semifinals of the Champions League.
It should have few problems qualifying from a group which includes City, Germany's Borussia Monchengladbach and Scottish champion Celtic.
And don't forget Atletico Madrid -- a finalist twice in the past three years. Diego Simeone's side has suffered heartbreak on both occasions but will be a force to be reckoned with once again.
The Spanish side has been paired with Carlo Ancelotti's Bayern Munich, Dutch champion PSV Eindhoven and Russia's FC Rostov in Group D.
If there's one name nobody had ever predicted to be involved with the Champions League draw, it would be Leicester City.
The unfancied club stunned the sporting world last season by winning the English Premier League in some style -- finishing 10 points clear of its nearest rival.
It received a somewhat favorable draw, with Porto, Club Bruges and FC Copenhagen providing the opposition.
Midfielder Riyad Mahrez has become one of the most coveted players in European football, while Jamie Vardy was one of the outstanding goalscorers in the league last season.
Few give Claudio Ranieri's side much of a chance of going deep into the tournament after losing key midfielder N'Golo Kante to Chelsea and the team's stuttering start to the domestic campaign.
But as the club motto will tell you, "Foxes are never beaten."
Juventus reached the final in 2015 -- and while it might have lost Paul Pogba to Manchester United, the Italian champion remains a formidable prospect.
Beaten by Bayern Munich in the first knockout phase last year, Juventus will be aiming to improve after winning its fourth domestic title in succession.
The $99 million signing of Gonzalo Higuian a
nd the arrivals of Barcelona's Dani Alves and Roma's Miralem Pjanic should give plenty of reason for encouragement.
For the second season in a row, Massimiliano Allegri's side will face Spanish side Sevilla, as well as Lyon and Dinamo Zagreb.
The draw has thrown up a number of potentially entertaining clashes, with England's Arsenal set to take on French champion Paris Saint-Germain in Group A, which also includes FC Basel and Bulgarian side Ludogorets.
Benfica, which last won the competition in 1962 and has since finished as runner-up on five occasions, will fancy its chances of progressing through a group which includes Napoli, Dynamo Kiev and Besiktas.
Tottenham, which finished third in England last season, faces CSKA Moscow, Bayer Leverkusen and Monaco in Group E.
Group A: Paris Saint-Germain, Arsenal, FC Basel, Ludogorets.
Group B: Benfica, Napoli, Dynamo Kiev, Besiktas.
Group C: Barcelona, Manchester City, Borussia Monchengladbach, Celtic.
Group D: Bayern Munich, Atletico Madrid, PSV Eindhoven, FC Rostov.
Group E: CSKA Moscow, Bayer Leverkusen, Tottenham, Monaco.
Group F: Real Madrid, Borussia Dortmund, Sporting, Legia Warsaw.
Group G: Leicester City, Porto, Club Brugge, FC Copenhagen.
Group H: Juventus, Sevilla, Lyon, Dinamo Zagreb.