Manchester suicide bomber Salman Abedi phoned his mother just hours before blowing himself up at Manchester Arena on Monday night (local time).
A Libyan security source told BBC Newsnight Abedi called his brother in Libya, telling him to ask their mother to phone him back, the Telegraph reports.
"Forgive me," Abedi told his mother Samia Tabbal, Associated Press (AP) reports.
Libyan Special Deterrent Force spokesman Ahmed bin Salem told AP Abedi's mother and brother in Tripoli revealed the phone call when they were questioned.
Abedi "was giving farewell" when he called his mother from the UK, Mr bin Salem said.
The 22-year-old Manchester-born man, who was known to security services, killed 22 people and injured 64 others at Manchester Arena, which was packed with children and teenagers there to see US singer Ariana Grande.
His father, Ramadan Abedi, was arrested in Tripoli soon after, and has been accused of being a member of the al-Qaeda-backed Libyan Islamic Fighting Group in the 1990s. He has denied being part of the group.
Reports say Abedi's younger brother Hashim, who was also arrested in Tripoli, knew his brother was planning an attack in Manchester.
But his father claims he didn't know.
"I spoke to [Salman Abedi] about five days ago... there was nothing wrong, everything was normal," Ramadan Abedi told Reuters, moments before he was arrested in Tripoli.
A spokesman for the local counter-terrorism force said his brother Hashem Abedi was also arrested on suspicion of links with Islamic State, and was suspected of planning to carry out an attack in the Libyan capital.
The first arrest made in Britain on Tuesday was reported by British and US media to be Abedi's older brother, 23-year-old Ismail.
Reuters / Newshub.