An iron hand/fist in a velvet glove

An iron hand/fist in a velvet glove

Describes the situation where someone or something appears gentle, mild, or soft on the outside but actually possesses strength, authority, or firmness underneath.

As a parent, she employs an iron hand in a velvet glove approach, balancing love and discipline to raise responsible and respectful children.

Mr. Johnson managed his classroom with an iron fist in a velvet glove, fostering a supportive learning environment while swiftly addressing any disruptions or rule violations.