The Brazilian spent last season on loan at Atletico Madrid after being suspended by Wolfsburg coach Felix Magath when he walked out of a pre-match team meeting in May last year after learning he was not in the starting XI for the match against Hoffenheim.
He has returned to the club this summer and, with his hard work in pre-season, has played his way back into Magath's plans, and now he has turned to the fans with an apology.
"I know that I disappointed many of you at the end of the season before last, even though I was welcomed so warmly here in Wolfsburg," wrote the Brazilian in a letter published on his club's website.
"My family and I have always been happy here and now we are back living in our home together and hit is simply a good feeling.
"I apologised to our coach last season and I have learnt from my mistake."
Magath accepted his apology and said that he is pleased to have the 27-year-old back in his squad for the upcoming season.
"Diego is a Champions League player and a player of his class increases the chances of us reaching one of the top places in the table," he said.
"Diego will get the number 10 shirt. He is a central player who can bring his team mates into the game and score goals himself.
"As the playmaker, it will be his task to lead his team mates to their best performance."
Diego has also called for the fans to show the same understanding as Magath as he hopes to lead the club back into Europe next season having celebrated Europa League glory with Atletico last May.
"I am pleased that I am receiving a second, fair chance from Wolfsburg and my team mates," he said.
"I am very grateful for that and pleased that they have faith in me. I hope that you, dear fans, will also give me this second chance.
"I can promise you that I will want to be the player who helps lead the team into Europe this season."