Last summer, the forward returned to Stamford Bridge for a club-record fee of £97.5m, ending two successful years at San Siro.
However, since the 29-year-old gave an interview to Italian media in December citing his unhappiness at Stamford Bridge, speculation has persisted over his future.
Although Inter have never been in any position to re-sign their former player on a permanent deal, it has long been suggested that a compromise could be found regarding a loan agreement.
After weeks of speculation, Chelsea have now confirmed that the Belgium international has started a second spell at the Serie A outfit.
While an article on the official club website gives limited details, it has been widely reported that Lukaku has returned to Italy on a straight loan deal.
Speaking after Inter also confirmed the deal, Lukaku said: "I'm back baby. I'm very happy. Remember three years ago when we were here? Good to be back.
"That's what we are here for (to score lots of goals), I keep my promises you know that. Thanks for having me. Forza, Inter!"
Lukaku is returning to a club where he scored 64 goals across two seasons between 2019 and 2021, 47 of which came in Serie A fixtures.
During that period, he played a key role in ending Inter's 11-year wait for another Serie A crown, but it became apparent during the 2021 summer transfer window that a second period at Chelsea may be on the horizon.
However, despite Chelsea breaking their transfer record to provide Thomas Tuchel with a world-class number nine, Lukaku only scored 15 times in 44 appearances.
Just eight of those strikes came in the Premier League, three being scored against Wolverhampton Wanderers and Leeds United in May when the top-flight crown was already well out of the club's grasp.
Earlier this week, it was reported that a second year at Inter may be in the offing if all parties can reach an agreement at the end of the season. body check tags ::