England international Tomori arrives at the Stadio San Siro as Milan look to bolster their defensive options, having lost Simon Kjaer and Alessio Romagnoli to injuries already at various points this season.
The Rossoneri took to their official website on Friday to announce the move for the 23-year-old, whilst confirming that an option is in place to convert the move into a permanent transfer in June.
Tomori has struggled to break into the first team at Stamford Bridge this season, with just a single Premier League outing for Chelsea in addition to three appearances across the FA Cup and League Cup.
Tomori, who made his international debut for England against Kosovo in November 2019, will wear the No. 23 shirt at Milan.