Guardiola opted against renewing his contract at Barca towards the end of the 2011/12 campaign after a trophy-laden spell at the club with whom he made his name as a player.
Having claimed three La Liga titles, two Copa del Reys, two Fifa Club World Cups and two Champions League crowns as coach, he cited fatigue for his decision to walk away.
After a year-long sabbatical in New York, he returned as boss of Bayern Munich for the start of the 2013/14 campaign and was quick to maintain the Bavarian club's dominance of German football.
Bayern have never been drawn against Barca during that time, denying Guardiola the chance to go back.
He was present on Wednesday, however, to see Barca's last-16 second leg against the English champions. The 44-year-old was captured by television cameras sitting in the stand with his father and personal assistant, former Spanish water polo player Manel Estiarte.
At half-time he gave his assessment of the opening 45 minutes to Catalunya Radio: "[Lionel] Messi is very good, very good. It’s a real luxury to watch him. The Barca players are very good and they are having a great season. They have played well and created a lot of chances. Let’s see what the draw brings.”
“It’s a great game we are watching. I hadn’t been back here for a while and I feel really good to be watching the game in the stands. It’s very special.”
Barca went on to win the game 1-0 to advance 3-1 on aggregate.
Bayern are already through to the quarter-finals after a 7-0 aggregate victory over Shakhtar Donetsk.