Have you ever learned something (a music instrument, a language, a sport, etc.) 'in secret' to surprise a loved one?
To surprise that loved one because he/she speaks that language that you learned, plays the same instrument that you learned to play.
My father, for example, plays the accordeon, and sometimes I want to take lessons, without him knowing, and then in some months/a year, surprise him by taking his accordeon and play him a song.
Have you done such a thing ever?