Mr Mohamed, a British resident, claims he was tortured
A British resident detained at Guantanamo Bay for more than four years is on his way back to the UK.
Ethiopian-born Binyam Mohamed, 30, says he was tortured while being held in custody on suspicion of terrorism.
The US had accused him of being part of a plot to detonate a bomb in America, but the charges were dropped last year.
Mr Mohamed's sister Zuhra said she was "so glad and so happy". His lawyer said he hoped the British government would allow his "immediate release".
The Foreign Office confirmed that Mr Mohamed's flight would land in the UK later on Monday.
Legal charity Reprieve, which has represented him, said he would be met by a doctor and his lawyers, as well as family and friends.
Director Clive Stafford Smith said: "He is a victim who has suffered more than any human being should ever suffer.
"He just wants to go somewhere very quiet and try to recover. Every moment that he is held compounds the abuse he has endured."
Mr Stafford Smith said Mr Mohamed wanted to thank all those in Britain who had worked to secure his release.
His sister Zuhra added: "I am so glad and so happy, more than words can express. I am so thankful for everything that was done for Binyam to make this day come true."
The BBC's security correspondent Gordon Corera said previous Guantanamo Bay detainees had been questioned by police upon their return to the UK.
The US had accused Mr Mohamed of involvement in a plot to detonate a "dirty bomb", but the charges were dropped in October.
Mr Mohamed says he was tortured into falsely confessing to terrorism and accuses British MI5 officers of complicity in his abuse.
He alleges he was secretly flown from Pakistan to Morocco and tortured before being moved to Afghanistan and on to Guantanamo Bay.
The UK attorney general is consulting the director of public prosecutions over whether to order a criminal investigation into the torture claims.
On Sunday, a Pentagon spokesman, US Navy Cmdr Jeffrey Gordon, said: "As a matter of long-standing policy, we do not discuss detainee transfers and releases until they are completed."
Mr Mohamed had lived in the UK from the age of 15, before being arrested in Pakistan in 2002.
Earlier this year he went on a month-long hunger strike at Guantanamo and his legal team said he was "close to starvation".
But last weekend he was declared well enough to travel back to the UK by a team of British officials who had visited him.
Lord Carlile, the UK's independent reviewer of terror laws, has said he believes that Mr Mohamed will now be "given every opportunity, subject to the law, to integrate himself back" into society.
His lawyers insist he poses no risk to the UK.