The former Miami Heat forward confirmed his decision yesterday, four years after leaving the team.
The head coach, who was appointed to an NBA coaching role for the first time in his career last month, told NBA.com: "I did not see this coming down the road. And I'll be honest with you, it was not a condition. Good things come to those who wait.
"I really don't want to talk in too much detail right now. It's not appropriate. I do want to say that to have the opportunity to coach the best player in the world is a blessing I would wish for everyone. And I know that because of the type of player he is and the type of man he is, our team will be better for it in every respect.
"It's just been a series of peaks without valleys. But I'm old enough and experienced enough to know that they come, too. I kind of feel like I'm jumping from mountaintop to mountaintop. But I know full well that it doesn't stay like that forever."
James won two NBA titles during his four-year spell with the Heat.