In a bid to reunite Allan and Carlo Ancelotti, Everton on Saturday signed the Brazilian midfielder from Napoli.
The transfer fee was not disclosed by the two clubs but media reports estimated it at 21 million pounds ($27.8 million).
The 29-year-old Allan played 61 games under Ancelotti when the Everton coach was in charge at Napoli.
"It is a real pleasure to sign for Everton," he said after agreeing a three-year contract at Goodison Park.
"It is a club with a rich history in the Premier League, has real ambition and then there is professor Ancelotti.
"He has done everything possible to bring me here. It is the size of the club and the name of the coach which means you don't think twice about coming to Everton."
Allan, who has won nine caps for Brazil, was with Napoli for five years after previously spending three years with Italian rival Udinese.
He and his new Everton team-mate Richarlison were part of the Brazil squad that won the Copa America on home soil last year.
"A strong part of my game is marking and the desire going in to win absolutely every ball," Allan said.
"I believe with my desire I can put in really good performances to win the fans over and I hope to win things?as well. There will be a tremendous amount of dedication from me."
Allan played more than 200 times for Napoli and featured in all 38 Serie A matches in 2017-18 when the club totaled 91 points to finish a close second to Juventus.
Everton starts its league campaign with a trip to Tottenham on September 13.