The 22-year-old sensation agreed last week to join Dortmund at the end of the season after the Bundesliga title holders tabled a €17.5 million bid.
Bayern Munich were also known to be interested in Reus, but the Germany international is confident that a move to Westfalenstadion was the best for his career.
"There I see a better chance to play internationally," Reus told reporters. "Dortmund are the best club for me."
Reus maintains he has a good relationship with Gladbach, where he has been since 2009.
"We are a great bunch, blend together very well and will play a good second half of the season," he said.
"I have learned a lot a lot in my three years at Gladbach and developed a feeling for what is best for me. I owe the club a lot."
Gladbach are currently fourth in the Bundesliga standings, four points behind leaders Bayern Munich, whom they will face when the league resumes on January 20.
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