The former Porto boss unveiled ex-Blues midfielder Di Matteo during his first press conference since succeeding Carlo Ancelotti.
The club also revealed the news with their official Twitter feed reading: "AVB confirms Roberto Di Matteo returns to Chelsea as assistant first-team coach."
Villas-Boas spoke of Di Matteo's appointment when asked about what brand of football he hoped to bring to the club.
He said: "If you see the technical staff in front of me, and my appointment of Roberto, these are people who like the quality of the game and have a philosophy.
"It's not just a case of winning it's a case of flair. Everyone likes attacking football and the Premier League has a certain amount of goals in every game and it should be an entertaining game for the fans and that is what we will look to do."
The 33-year-old also insisted he is not fazed by the demands for success placed on managers at Stamford Bridge. Ancelotti was sacked just a year after he had guided the club to their first league and cup double, while not even Mourinho could deliver the Champions League for owner Roman Abramovich.
But Villas-Boas says the challenge of consistently securing silverware is one he will relish.
He said: "The expectations are for the maximum. We want to win trophies, that is the challenge we face day by day in any business. Everyone wants to be the best and win something and the challenge is to win as soon as possible and to build a platform for the future.
"This is nothing different from any other club, the challenge in your everyday life is to be successful in what you do and that is the challenge I face here."
Source: PA
Source: PA