Following the 2-0 win, PSG's players assembled on the pitch and had a photo taken of them mimicking Haaland's 'lotus' celebration.
Germany fullback Kehrer explained to Kicker: "There were a few provocations from the opponent after the first match. That's when it comes to revenge.
"You may argue whether it has to be this way or not, but these are feelings and you don't have to hide them."
Kehrer spent six years with Dortmund's rivals Schalke and added: "That's why I was extra motivated. There is nothing better than beating Dortmund."