曾经的公主裙
[céng jīng de gōng zhŭ qún]
It means 'the former princess dress'. This can mean different things depending on context, but generally speaking, it's usually used to denote a woman who once dreamed of being like a fairy tale princess complete with ball gown, and now those times (of innocence or youth, etc.) have passed her by - so it reflects on past dreams, memories and how far she has progressed from childhood naivete and fantasies towards a real-world maturity.