at heart

English

In spirit; according to one's beliefs, views or feelings; deep down, fundamentally, really.
Synonyms: at bottom, essentially; see also Thesaurus:fundamentally

I’m a vegan at heart – the thought of the death of animals for my food is abhorrent.

My dad may be old on the outside, but he’s young at heart; he plays video games every now and then to improve his coordination.
- 2019 August 14, A. A. Dowd, “Good Boys Puts a Tween Spin on the R-rated Teen Comedy, to Mostly Funny Effect”, in The A.V. Club‎^[1], archived from the original on 4 March 2021:
  One could argue, of course, that most comedies about the risqué misadventures of teenagers are actually pretty wholesome. Horny hits like American Pie and last year's Blockers are, at heart, sweet coming-of-age stories, secretly reassuring everyone that the kids are all right—that no matter how many f-bombs they drop, no matter how raunchy their MPAA-antagonizing hijinks get, they're really just fumbling their inexperienced way through normal rites of passage.
Wished earnestly for; held in high esteem.
I always have your best interests at heart.

in spirit; according to one's beliefs, views or feelings