The 22-year-old spent last year on loan at the Stadio Olimpico Grande and made 32 appearances for the club across all competitions, firmly establishing himself in Walter Mazzarris first-team.
Despite the prospect of having senior chances in west London, however, Chelsea have now confirmed that Ainas move to Torino has been made permanent.
Aina has spent over 10 years working through Chelseas academy system and hes been part of a number of their outstanding youth teams, winning two FA Youth Cups and two UEFA Youth League titles.
Making his senior debut for the club in 2016, Aina went on to make six first-team appearances before deciding to join Torino on loan last summer. He scored one goal and picked up three assists whilst at the club, helping Il Toro finish ahead of Lazio and Sampdoria.
Although Chelsea havent confirmed how much theyve pocketed as a result of Ainas sale, its believed that the defender will cost Torino €10m this summer as a result of a purchase option in his loan deal.
The Nigeria international becomes Chelseas second sale of the summer after announcing Eden Hazards move to Real Madrid, while the likes of Gary Cahill, Todd Kane and goalkeeper Eduardo will become free agents.
Torino president Urbano Cairo has confirmed that Ola Aina has left Chelsea after his £8.9m (€10m) option was exercised. I have been reporting their intent to do so since January. We should see the social media announcements on official accounts soon. #CFC
— Nizaar Kinsella (@NizaarKinsella) June 10, 2019
Borussia Dortmunds Christian Pulisic remains the only new face who will come through the door at Stamford Bridge as a result of the clubs transfer ban, but players like Mario Pasalic, Mason Mount and Tiemoué Bakayoko will be returning for loan spells away.