Grimoald then made an agreement with the Avars who invaded the duchy and killed Lupus. They then refused to withdraw and continued their raids until Grimoald himself intervened and managed to induce them to return to Pannonia.
After Lupus' death at the hands of the invading Avars, Grimoald negotiated a peace treaty with them, but when they failed to leave, he took matters into his own hands and persuaded them to retreat back to their homeland in Pannonia.