Chris Smalling has completed his move to Roma after the Italian side came to terms on a deal with Manchester United late on Monday, the Premier League club announced.
The two sides had been in negotiations for the defender through the summer, with United insisting that Roma had not met their valuation of the defender.
On Monday, though, the two sides came to terms on a deal, with Smalling heading back to Italy in a transfer worth €15m (£13.6m/$17.7m) plus add ons.
The defender has signed a three-year deal that will keep him with the club until 2023.
“Nothing in life worth having comes easy,” Smalling said. “My head and my heart has always been in Rome. I am delighted to now be yours. Daje Roma!”
“We are pleased to be able to welcome Chris back to the club, as one of the pillars of our squad,” added Guido Fienga, the club’s CEO.
“I would like to thank Manchester United for the consideration they have shown throughout this strenuous and lengthy negotiation.”
Smalling impressed during his loan spell with the Italian side last season, making 37 appearances in all competitions while scoring three goals in Serie A.
The defender had been pushing for the move all summer, but was forced to wait it out as the two clubs negotiated his transfer.
He is now set to rejoin the Serie A side, who have earned four points from their first three league matches this season.
Smalling initially came up with Maidstone United and then Fulham, before catching the eye of Man Utd with the latter by making 18 appearances in all competitions in 2009-10.
He signed with Man Utd in January 2010 and joined up with the club that summer, going on to make 323 appearances across nine seasons with the club.
During his time at Old Trafford, Smalling won two Premier League titles, an FA Cup, a Carabao Cup and a Europa League crown while also establishing himself at the international level.
The 30-year-old defender has earned 31 caps for England, having been a part of the Three Lions squad at the 2014 World Cup in Brazil and the 2016 Euros in France.
Smalling's departure comes shortly after Man Utd confirmed another defensive addition in full-back Alex Telles, who became the club's second signing of the summer after Dutch midfielder Donny van de Beek.
The club is also expected to complete a deal for Edinson Cavani, who appears set to join Ole Gunnar Solskjaer's side soon.
The Red Devils are set to face Newcastle following the international break before then turning their focus towards Paris Saint-Germain in the Champions League.
Roma, meanwhile, will host Benevento when Serie A play resumes.