The pair didn't see eye to eye when Ibra was at the Nou Camp.
Guardiola said: "Ibra had an extraordinary year in Barcelona, helping us in the Liga and the Champions League. Without him we would not have achieved everything we did. He has always done well in every club and I have fond memories of his time at Barça.
"It will not be Ibrahimovic against Barcelona, as we are playing against Milan, the club with the most international trophies in the world. Coming to play at San Siro is an honour.
"If we don't perform against Milan in the quarter-finals, we won't qualify. We know that we must do our best, aware that we might or might not go through to the next round, so it is a big test for us.
"Both these sides have great champions, so the team with the most psychological strength over the two legs will qualify. We want to take control of the game and hold on to it in every moment, but it is understandable to go out against Milan."