The 23-year-old left Borussia Park last summer for Signal Iduna Park, where he started his career as a youngster, and has revealed that he still holds a place in his heart for his old employers.
"Gladbach will always be something special for me!" he told Bild.
"With Gladbach, I became part of the national team, played my first Bundesliga match and scored my first Bundesliga goal. I will never forget them, and I am very grateful towards the entire club."
Reus has been a huge hit since rejoining the Schwarzgelben, and the Germany international believes that his outlook has helped him be successful, along with the support of his colleagues.
"I am generally an optimistic person," he continued.
"Of course I believed that everything would be fine. My team have also made it very easy for me, and I have all the support I need!"
Mario Gotze set up two of Reus’ three goals against Frankfurt at the weekend, and Reus has admitted that he does not know why the pair combine so well.
He added: "Some things are just as they are, and that's good!"
Reus scored twice when Dortmund beat Gladbach 5-0 at the end of September at Signal Iduna Park.