Guest of Bride or Groom'

My friend’s son, Kelly, seemed young to be an usher at a wedding, but he was quickly coached in wedding protocol. A veteran usher instructed Kelly to ask the person he was escorting, “Are you a guest of the bride or groom?” to know where to seat them.
Imagine our surprise when we heard Kelly ask, as he graciously offered his arm to the first arrival, “Madam, whose side are you on?”