How to put the inner div of a nested div structure into a new row using flex box?

Question

I want the inner div (Mem 3) in a new row, below Mem 1, and I don't want to change the div structure at all costs. please help.

Like this =>

.flex-container {
  display: flex;
  flex-wrap: wrap;
}

.flex-child {
  border: solid blue;
}

.flex-fgc {
  border: solid blue;
}

.flex-inner-gc {
  border: solid blue;
}

<div class='flex-container'>
  <div class='flex-child'>
    Mem 1
  </div>
  <div class='flex-fgc'>
    <div>
      Mem 2
    </div>
    <div class='flex-inner-gc'>
      Mem 3
    </div>
  </div>
</div>

I tried "flex: 1 1 100;" for flex-inner-gc.

Answer 1

float can easily do this.

.flex-child {
  border: solid blue;
  float: left;
}

.flex-fgc > * {
  float: left;
  border: solid blue;
}

.flex-inner-gc {
  clear: both;
}

<div class='flex-container'>
  <div class='flex-child'>
    Mem 1
  </div>
  <div class='flex-fgc'>
    <div>
      Mem 2
    </div>
    <div class='flex-inner-gc'>
      Mem 3
    </div>
  </div>
</div>