In Qing palace dramas the princes are always calling out 'Imperial Father'.
Tips
culture
阿玛 (āmǎ) is Manchu for 'father'. The Qing imperial family kept Manchu kinship terms, so princes addressed the emperor as 皇阿玛 rather than 父皇. The word is now familiar mainly through TV dramas.
register
Historical/dramatic only. Never used in modern speech.