7. Romelu Lukaku (to Everton for £32m, 2014/15)
The Belgium striker exploded at Goodison Park, scoring 25 goals in the 2016/17 season. He was close to returning to Chelsea after that campaign but ultimately chose Man United. Now, he's plying his trade at Inter Milan and has so far scored 51 goals in 73 games - an elite level.
6. Nemanja Matic (to Man United for £40m, 2017/18)
The Serb followed Jose Mourinho to Man United and in his first season at Old Trafford, he was as important there as he had been for Antonio Conte in his triumphant first season. He's now 32 years old and an important squad player despite some justifiable concerns over his speed.
5. Juan Mata (to Man United for £40m, 2013/14)
Mata was Chelsea's Player of the Year in his first two seasons at the Bridge - but then, along came Jose who let him go to United in the middle of the 2013/14 campaign. He was a regular starter for the Red Devils - until Mourinho followed him there as well. Now, the 32-year-old is quite far down the pecking order.
4. David Luiz (to PSG for £45m, 2014/15)
The wayward centre-back won 7 domestic trophies in two years in France before returning to Chelsea and winning his first Premier League title. After that there was a falling out with Conte, a resurgence under Maurizio Sarri and an honest talk with Frank Lampard that led to his exit to Arsenal - and it looks like a masterstroke from the Blues.
3. Oscar (to Shanghai SIPG for £54m, 2016/17)
The 29-year-old is still in China where he has won two trophies, including the Chinese Super League in 2018. He has not played for Brazil since he left Chelsea, though. Besides, he might have to leave China soon due to the new salary caps that will be introduced from the next season - no one will pay him £400,000 a week anymore.
2. Diego Costa (to Atletico Madrid for £54m, 2017/18)
Chelsea got the better side of the deal there: Costa has never scored more than 7 goals in a season anymore. He's now left Atletico as a free agent and remains without a club.
1. Eden Hazard (to Real Madrid for £104m, 2019/20)
Eden has had his fair share of injuries after joining the La Liga giants - so much so that there are rumours of people inside Real Madrid being tired of him underperforming. So far Hazard has only scored 3 goals and played 32 games in all competitions for his new club - he had better figures in each of his seasons at Chelsea.
(all fees via Transfermarkt)
