Childebert III the Adopted (Childebertus Adoptivus) was a Frankish king. He was a son of the Mayor of the Palace Grimoald the Elder and was thus a grandson of Pepin of Landen. He was adopted by King Sigebert III and Queen Chimnechild.
When Sigebert III died in 656, Grimoald had Sigebert’s biological son Dagobert II shorn of hair and sent him to an Irish monastery and then proclaimed Childebert king of Austrasia.
Grimoald, Childebert and Ansegisel (who had married the daughter of Pepin of Landen) were finally seized and turned over to the king of Neustria, Clovis II, who had them killed.