Aspen and his sister Princess Alder made their first appearance in Fables #91. They were created as a sign of a pact, of Geppetto's alliances with Grandfather Oak to be his bodyguards. While both were naked, none of the Fables at the Farm or the refugees at Fabletown seemed to pay mind to them. They only started becoming troublesome as Geppetto was trying to take control of the Farm and most likely of Fabletown. But even then, they are not entirely loyal to him. As they state to him, they will protect him if some should harm him. But if he should feel insulted, they are not at liberty to do a thing for him.
When Rose Red, recovered from her depression, she took back control of the Farm. And one of her first instructions was for Prince Aspen and Alder to return to the woods, as they were not necessary and troublesome. When both the siblings and Geppetto began to threaten her, she held her ground. Furthermore, reminded the siblings if they didn't behave, she'd send Clara to burn Grandfather Oak; thus killing them. Though Alder, herself, pleaded with Rose Red to let them stay. Rose refused and told her for one last time to return to Grandfather Oak. It appears he and Alder did as they were told and are probably trees again.