When does The Grim Adventures of Billy & Mandy return?

Billy & Mandy began as a segment on Grim & Evil, from which it was a spin-off, along with sister series Evil Con Carne, on August 24, 2001. The series aired (as a separate series) from June 13, 2003, to October 12, 2008, on Cartoon Network. It is centered around the exploits of Billy, an idiotic and happy-go-lucky boy; Mandy, a cynical, cold-hearted and grumpy girl; and Grim, a Jamaican-accented Reaper. The pair use Grim's supernatural abilities and powers to venture into supernatural locations or environments.
The series is centered around the exploits of Billy (Richard Steven Horvitz), an idiotic and happy-go-lucky boy; Mandy (Grey DeLisle), a cynical, cold-hearted and grumpy girl; and Grim (Greg Eagles), a Jamaican-accented Reaper. Billy and Mandy use Grim's supernatural abilities to venture into supernatural locations or environments, such as the Underworld, or the Netherworld, inhabited by an assortment of grotesque monstrous beasts. Famed fictional monsters including Dracula, the Wolfman, and the bogeyman are also comically depicted in the series.