France striker Olivier Giroud thanked Chelsea for "special moments" as he underwent a medical ahead of a move to AC Milan.
World Cup-winner Giroud scored 39 goals in 119 games in all competitions for Chelsea and helped the London outfit claim the Champions League, Europa League and FA Cup since joining them from Arsenal in 2018.
"To all the Blues, to my teammates, to all my coaches, to the whole club, a huge thank you for these special moments," Giroud tweeted.
"I'm starting a new journey with a light and happy heart. Our victories in the FA Cup, Europa League and Champions League have been magnificent."
The 34-year-old joined Chelsea from Arsenal for £18 million ($24.79m) in January 2018, six years after signing him from the Ligue 1 title-winning Montpellier side for £10.8m, and had a year left on his contract at Stamford Bridge.
He started only eight Premier League games for Chelsea last season following the arrival of German forwards Kai Havertz and Timo Werner.
He was part of France's underwhelming Euro 2020 campaign as they were knocked out by Switzerland on penalties at the round-of-16 stage following a 3-3 draw after extra-time.
Giroud arrived at Milan's La Madonnina clinic on Friday to undergo a medical. Reports added Milan would pay around $1.18m for the player who is expected to sign a two-year deal, with an extra $1.2m in bonuses subject to a number of appearances and qualification for the Champions League.
In June, Milan signed Chelsea's Fikayo Tomori on a permanent transfer after the defender spent the second half of the 2020-21 season with the Italian side on loan.
Milan, who finished second in Serie A last season, begin their 2021-22 league campaign away to Sampdoria on August 22.