kindly in appearance but unfathomable at heart
He is kind in appearance but unpredictable in heart. It's the same as "deep feeling".
Idioms and allusions
Source: Qing Dynasty, Chen Menglei's "friendship breaking book": "swear to heaven, thick appearance and profound writing, enough to move."
Discrimination of words
Usage: as predicate, attribute; refers to the appearance of kindness, the heart is unpredictable.
kindly in appearance but unfathomable at heart
a student 's long years of academic studies - shí zǎi hán chuāng
ask after the people 's sufferings with deep concern - hán liǎo wèn jí
a pasture on which cattle can graze - cháng lín fēng cǎo
give a swift glance and practise fawning - yān shì mèi xíng
No shoes in melon field, no crown under plum - guā tián bù nà lǚ,lǐ xià bù zhěng guān