Paul Mosley from Derby appears at the city's magistrates court charged in connection with the murder of six children at a house fire in May.
Mosley, 45 was last night charged with the murders of Jade Philpott, 10, and her brothers John, nine, Jack, eight, Jesse, six, Jayden, five, and 13-year-old Duwayne, Derbyshire Police said.
The children died after a blaze engulfed their home in Victory Road, Allenton, Derby, on 11 May. Their parents, Mick Philpott, 55, and his 31-year-old wife Mairead, have also been charged with all six murders. They are next due in court on Thursday.
Mosley was arrested on Monday afternoon by officers investigating the deaths along with a 49-year-old man, who has since been released without charge, police said.
Assistant Chief Constable Steve Cotterill said: "Three people have now been charged with the murder of these children.
"This man stands accused alongside Michael and Mairead Philpott. Our investigation will continue in an effort to gain justice for the children."
Mick and Mairead Philpott, who are both in custody and did not attend their children's funerals in June, will appear before Nottingham crown court on Thursday, where they are expected to enter pleas to each of the six murder charges.