The spandex-clad rock group split in 2006 when Justin left to battle drink and drug problems and the warring siblings have not spoken since.
However, drummer Ed Graham has managed to heal the rift, with the help of his son, who was born earlier this year.
A source told The Sun newspaper: "Dan and Justin's falling out was a very bitter affair. They didn't speak for almost half a decade. But spending time with Ed and his family has reminded them all how close they once were."
Frontman Justin and guitarist Dan have now buried the hatchet and are busily planning the band's comeback.
The band, which also features Richie Edwards on bass guitar, have begun rehearsals and are planning to start touring next year.
Justin - who went on to form the group Hot Leg after The Darkness split - has previously spoken of his pride at his first band's achievements.
He said: "I'm actually quite proud of the work that we did - not all of the work we did.
"When I think of what we achieved in a year, we went from opening Glastonbury to headlining Reading and I don't know if many people can say that really."