Invidiam tamen suscepti nominis C. P. imperatoribus super hoc indignantibus magnâ tulit patientiâ, vicitque eorum contumaciam ... mittendo ad eos crebras legationes, et in epistolis fratres eos appellando. (Eginhard, c. 28, p. 128).
Perhaps it was on their account that, like Augustus, he affected some reluctance to receive the empire.