How populate 2nd form opened with value from selected record in 1st form

I have a form which has a subform.  On the subform is a numeric field named ID.  This field is a hyperlink.  When the user clicks it a 2nd form opens.  On this 2nd form is a field also named ID.  I want the value of the field on the 2nd form to be the same value as the ID field on the 1st form (subform).

But it has to get the value from the SELECTED record on the 1st form.

I have this in the default value of the 2nd form but it isn't working because its not using the selected record.  How do I fix this?

=[Forms]![subfrmPets]![txtID]