The second of the Hazards joined Chelsea soon after the first one did, though their career paths since could have barely been any more different. Thorgan went out on loan for two years to Zulte Waregem before joining Borussia Mönchengladbach, also on loan in 2014. That move was made permanent not a year later and he's been there ever since. Lately, rumors have linked him to a move back to Chelsea, through either a buy-back clause (which may or may not exist) or perhaps some sort of other understanding, like what surely allowed Chelsea to re-sign Nemanja Matić on the cheap a couple years ago.
In any case, Thorgan Hazard's success is yet more ammunition for those who like to take shots at Chelsea's handling of youth prospects, but for the kid himself, it's all rather understandable. This won't make for good headlines, Thorgan!
"Of course, it helped that Chelsea also signed Eden, but it is not like they just sign every player's brother. [Frank] Lampard and [John] Terry's brothers never played for Chelsea. They signed me because I showed potential. They had to pay Lens a transfer fee to get me. And they were right. I might not be following the same path as Eden, but I am improving step by step."
"I knew I would not stay at Chelsea when I signed for them. It was a great opportunity to join such a big club, but I knew I needed regular playing time to show what I could do."
"Chelsea like to buy young players and then slowly get them ready. All the young players like Kevin De Bruyne, Charly Musonda and Romelu Lukaku were shipped out on loan. You need regular playing time at that age. Maybe Chelsea now regret their decision not to give De Bruyne and Lukaku more chances, I don't know."
-Thorgan Hazard; source: Het Nieuwsblad via ESPN
I mean, Chelsea, as a collective probably do. Jose Mourinho, who held the keys to such opportunities at the time, probably doesn't.
Both Lukaku and De Bruyne have talked about how whatever's happened, happened for a reason (be that their personal development or decisions made by the decision-makers) and it's not like we can change the past, so let's just concentrate on the present and the future — a future that may yet include a return to Chelsea for any of the three. You never know in football, after all, and if rumors are to be believed, Chelsea were after Lukaku already this summer.