Allegri was named as Juventus coach in July after the shock resignation of Antonio Conte, who had led the team to three successive Serie A titles in as many seasons in charge and made them the dominant force in Serie A.
Out of a job at the time, he was a convenient option for Juventus although their fans were certainly not impressed and greeted the appointment with protests.
AC Milan had dismissed Allegri halfway through last season after a 4-3 defeat to Serie A newcomers Sassuolo on a wet January evening left them languishing in eleventh place with only five wins in 19 outings.
But Allegri hardly seemed to be to blame for the fiasco, having seen his top players, including Thiago Silva and Zlatan Ibrahimovic, sold off over the previous 18 months.
The 47-year-old was swimming against the tide against Milan, a club struggling to come to terms with the harsh, austerity-strapped new reality of Italian football.
He had agreed to help the club rebuild the team with talented young players and had led them to a respectable third in 2012/13, winning the backing of the Ultras.
Instead of youth, however, Milan's leadership seemed all at sea and provided Allegri with a motley assortment of journeyman professionals and players clearly past their best such as Michael Essien and Kaka.
It had all been very different in his first two seasons when Allegri led Milan to the Serie A title in his debut season, followed by a second place the following year.
Deadpan and unflappable, he proved adept at handling a powder keg of a dressing room which had included unpredictable talents such as, at various points, Ibrahimovic, Robinho, Mario Balotelli and Kevin-Prince Boateng.
The one player Allegri felt he could not deal with was Brazilian Ronaldinho, well-known for his partying lifestyle, who returned to his homeland.
Andrea Pirlo, meanwhile, left at the end of Allegri's first season in charge and has since enjoyed three seasons of unmitigated brilliance at Juventus and a quirk of fate has now reunited the pair.
"I have always enjoyed a good relationship with him," said Allegri on his official presentation.
"Andrea is still, a champion. When he was at Milan with me, he went through that season which wasn't particularly lucky for him considering that it was dogged by injuries. But, he always played when he was fit.
"In football sometimes you think that things might go one way but eventually they take an unexpected turn or head in another direction. As I have explained a thousand times, in the end it just happened. The club, Andrea and I met and he decided to join Juventus."
Allegri now finds himself at a club that is going in the opposite direction to Milan.
Whereas Milan play in the fading, municipally-owned San Siro, Juventus are the only Serie A club to own their stadium and the only team to routinely play in front of a full house at home.
With only a few days to go until the end of the transfer window, Juventus have managed to retain all their key players including Pirlo, midfielders Arturo Vidal and Paul Pogba and front pair of Carlos Tevez and Fernando Llorente.
Allegri knows that he will have no excuses this time, although it is not going to be easy to maintain Juve's remarkable recent form.
The passionate Conte is a tough act to replace and he made it clear last season that he felt that Juventus had reached their peak in winning Serie A with a record 102 points.
AS Roma, Napoli and Fiorentina all look like serious contenders and may well feel that Juventus are vulnerable without Conte.
But midfielder Claudio Marchisio said that Conte's departure could reinvigorate the squad who may have suffered enough of his infamous dressing-room tirades.
"It's up to us to show now that, after three years of Conte, we can still do it without his shouting," he told Gazzetta dello Sport.
"We've got better in these three years and Allegri has inherited a squad which has come a long way. Allegri is calm and has his own character but that doesn't mean to say we work less.
"It gets harder to win every year but the arrival of a new coach has given us more motivation. It's wrong to talk about the end of a cycle.
"Our aim is to improve where we failed before and Allegri is the right coach to re-launch us."