In 1489 DR, the arrival of Claugiyliamatar corrupted Ishaldra and her treant bodyguard. Thus Whitchthorn, who had become king, unleashed his evil against the desecrator of the forest, but Old Gnawbones was too powerful for him.
Ultimately, an adventuring party hired to defeat Old Gnawbones gained an audience with the fey king. Whitchthorn agreed to give his help in order to defeat the green dragon, but only if one of the adventurers made an oath with him. Presumably, the adventurers agreed to the pact.