Salah Abdeslam, sentenced to life in jail over the 2015 Paris jihadist attacks, was removed from his Belgian prison cell on Wednesday and transferred back to France.
Found guilty in Belgium last year of planning subsequent 2016 attacks in Brussels, his transfer back to continue serving out his French prison sentence had been blocked by an appeals court on human rights grounds.
The Belgian federal prosecutor's office confirmed the transfer -- first announced by Abdeslam's lawyer -- saying he was taken from a Brussels jail to the border and handed over to French authorities.
After the Paris attacks, Abdeslam fled to Brussels where he was arrested in March 2016, days before suicide attacks that killed 32 and injured hundreds at Brussels airport and a metro station.
Both massacres were part of a wave of attacks claimed by the Islamic State group in Europe.
Since 2016, Abdeslam has been detained mostly in France, but his lawyers have argued he should be allowed to serve his sentence in Belgium, where he grew up and has family ties despite holding French citizenship.
Abdeslam's lawyer Delphine Paci slammed the transfer as "a flagrant violation of the rule of law".
Read more on FRANCE 24 English
Belgian court sentences terrorists behind 2016 Brussels bombings
Belgian court finds Paris attacker Salah Abdeslam guilty of murder in 2016 Brussels bombings
Landmark Paris attacks trial leaves riddles unsolved, tears unnumbered