Thorgan Hazard signed for the Blues back in 2012, but says that he always knew that his future lied elsewhere.
The 23-year-old spent his first two years on loan at Zulte Waregem before moving to Gladbach in 2014.
"I knew I would not stay at Chelsea when I signed for them," Hazard told 'Het Nieuwsblad'.
"It was a great opportunity to join such a big club, but I knew I needed regular playing time to show what I could do.
"Chelsea like to buy young players and then slowly get them ready. All the young players like Kevin De Bruyne, Charly Musonda and Romelu Lukaku were shipped out on loan. You need regular playing time at that age.
"Maybe Chelsea now regret their decision not to give De Bruyne and Lukaku more chances, I don't know".