Although this is not the commonly used version, it is the Official Forbes (Ancient) as recorded in Lord Lyon's Register of All Arms and Bearings in Scotland. (PRA 37/124) 2nd December 1949. STS notes: Lord Lyon includes the word 'Ancient' in register entry.
The Clan Forbes is said to originate from one Ochonochar, who slew a bear to gain possession of the Braes of Forbes in Aberdeenshire. The charter for the land was granted later in 1271.