Order by Function in dropdown

[Dan_Velus]

Hi There, 

I have a dropdown (EnumList) field in Table1 that uses a SELECT function to get the values from Table2. The data looks something like this:

Table1

First Name	Last Name	Full Name
John	Smith	John Smith
Angel	Boss	Angel Boss

I am trying to bring the above data into the EnumList on the Table2 form and I would like to sort the dropdown by [Last Name]. The SELECT query, I am trying looks like this:
ORDER BY(SELECT(Table1[Full Name], TRUE), [Last Name])

The error I am getting is, that the column [Last Name] doesn't exist. 

Could someone help me with this, please? Thank you so much.