Lukaku, 29, had a superb run with Inter after arriving at the club from Manchester United ahead of the 2019-20 season, scoring a combined 64 goals from 95 club appearances across two seasons.
His stellar play in Italy caught the attention of his former club from Stamford Bridge, which opted to bring him back for a club-record fee of £97.5million.
The Belgian's return to the Premier League was disappointing, regularly finding himself in of Chelsea's best XI even when healthy, finishing with just eight goals in 26 league games, prompting a £7m loan move back to the Serie A to try and recoup some of Chelsea's sunk cost.
During the kit unveiling, Lukaku was asked what the toughest challenge of his career has been, and he made it clear how he felt about his second stint with Chelsea.
"The one right now," he said. "You know, I left, it was a mistake.
"What we do in the locker room and on the pitch, the relationships we have with each other, that’s really important… it’s also right for people to see that our team is really united.
"Inter have given me the opportunity to play at a higher level in my career. I am really happy to wear this jersey, we hope to continue to grow like in the past years. We have to continue like this if we want to reach the goal."
Chelsea boss Thomas Tuchel may also share Lukaku's belief that he does not have a future with the London club, telling Sky Sports "I don't know if it's very likely" that he ever returns to Stamford Bridge after his loan.
"Given the fact he's just on loan, of course there's a chance," he said. "I don't know if it's very likely, but it's not on me to give an outlook on that.
"We decided together with the owners that we'd let (Lukaku) go. It was his wish to go, he had the possibility, we let him go.
"We brought now Raheem Sterling, which gives us a lot of flexibility, a lot of mobility, a lot of attacking options at the front, even if we don't recruit more players."