Project Kr also known as Superboy was a clone of Superman from Cadmus. The strand of DNA that Lex Luthor obtained from Superman was used to create him. Now, he's a weapon of mass destruction living in a tube in a CADMUS lab. Hes learned much from the scientists about the Earth and knowledge about it and the solar system. However, he had never seen the stars or the moon or the sun or the clear blue sky or the clouds or rain or anything. All he knew was metal... and his powers.

When Supergirl stumbles upon him, Kara mistakes him as an actual Kryptonian CADMUS had captured and freed him. Except he wasn't what she expected. With Superboy in tow, Kara leaves, and Lillian Luthor sees this perfect opportunity as a way to achieve her goal:

To destroy Supergirl.

What Lillian Luthor didn't expect was him to get close to her and her family. What she really didn't expect was for him to get a little too close to Kara as she liked it to be.