Close a form and pass data to the form that called it

I have a clock card form that can optionally open a quick-fill form that allows the user to specify a number of criteria, hit 'Fill' and it closes the subform to return to the original. There be an array passed (of some description) from the quick-fill form to the clock card form, this array will be analysed and a number of records created in a DataGridView.

On the original form I have this which launches the quick-fill:
private void btnFillEntries_Click(object sender, EventArgs e)
        {
            formClockCardFiller formCCF = new formClockCardFiller(currentWeek);
            formCCF.WindowState = FormWindowState.Normal;
            formCCF.ShowDialog(this.MdiParent);
        }

How do I fill the DataGridView once the form receives focus from the quick-fill form? This would be easier if I was creating a new form via a constructor, but in my case the calling form is already open. In the subform at OnLoad, do I create a reference to the calling form in some way?