The 36-year-old Gabon striker joined Marseille from Chelsea in 2022 and spent one seasons with the team before his departure to Al-Qadsiah in 2024.
He made a huge impact in his first spell with 30 goals and 11 assists in 51 matches in all competitions, and makes his return after another good goalscoring campaign, this time netting 21 goals in 36 games, alongside three assists for his now former Saudi Pro League club.
Aubameyang made his second debut for the club in a pre-season friendly 1-1 draw with Sevilla on Saturday.
De Zerbi said on Foot Africa: "Aubameyang really wanted to come back. It hurt us when he left. I wanted to send him on alone tonight so he could feel the love from the fans. He's still in great shape, and that doesn't take anything away from [Amine] Gouiri, who still has the advantage. We might even see them both together."
Upon returning to Marseille, Aubameyang told the club's website he was blown away by the fans' response.
He said: "I expected something from the fans; I'd been following social media. But honestly, not this much enthusiasm. I'm very happy and will be eternally grateful for this.
"I've always maintained good contact with the management and players. I spoke with sporting director Mehdi Benatia and president Pablo Longoria. They didn't need to convince me; I watched the matches last season. It was a quick decision.
"I had offers not only from Saudi Arabia but other teams, but I chose to return here. I experienced some powerful moments here, and that's something you can't buy," added the Gabonese international.
"Roberto De Zerbi was a key factor in my return. When I left, I spent two weeks with the coach. In training, I saw what was happening and that great things were coming. He didn't give up on me, he kept "pushing" me to come back, and that's good. I
"I'm back, and we'll do great things together. We need to try and compete with PSG and go as far as possible in the Champions League."