The 17-year-old, who has impressed in his first senior games in the Bundesliga this season, was a hot property in the summer.
And according to agent Philip Degen, a former Liverpool full back, the Reds were in line to sign Bellingham.
Degen, who works for a group of agents called SBE Management, told the Liverpool Echo: "It is one of the biggest victories for Dortmund [to sign Bellingham] because the challenge to get this player was very, very high and they had to fight for months.
"I know his agent, and I am a very good friend of him, and I know which kind of fight it was - every top club in Europe wanted to sign him.
"Dortmund made this challenge and they won it and it is the right step for me to get to a big star. Dortmund have shown before that they can develop players to a higher level and they can do very big steps, so it was the right decision.
"Even between the agents - and I know Mark, his agent very well - and I really like when people have a straight mind and they never forget from where they are coming.
"It was the right decision and the right move - that is clear."