The younger brother of the Manchester Arena suicide bomber will be charged with murder after being extradited to the UK, police say.
Officers escorted Hashem Abedi on a plane from Libya on Wednesday.
His brother, Salman Abedi, blew himself up at the end of a show by US singer Ariana Grande in May 2017, killing 22 people including seven children.
Britain issued an arrest warrant for Hashem six months later but it was only today that he was handed over to UK authorities.
Greater Manchester Police said he would appear at Westminster Magistrates' Court charged with the murder of the 22 victims, attempted murder of others and conspiracy to cause an explosion likely to endanger life.
"Since the Manchester Arena attack of 22nd May 2017, our thoughts have been with the families of those who lost loved ones and the hundreds who are struggling with serious physical injuries and deep psychological effects," said Ian Hopkins, chief constable of Greater Manchester Police.
"They have always been central to our investigation and will continue to be so at all times.
"I am now able to say that following application by the Crown Prosecution Service for the extradition of Hashem Abedi from Libya, that today he has been successfully extradited, for offences relating to the Manchester Arena attack.
"He was handed over by Libyan authorities to British police officers this morning. They escorted him on the flight back and he landed in the UK a short while ago.
"Greater Manchester Police officers have arrested Hashem Abedi for murder, attempted murder and conspiracy to cause an explosion likely to endanger life."
The two brothers were both born in Britain to Libyan parents who had fled Muammar Gaddafi's regime but returned to their native county in 2011 after he was overthrown.