Next Derry Girls instalment is a flashback to Ma Mary and Aunt Sarah's teen days 

Lisa McGee said she always wanted to write something based around the two sisters 

Episode 5 will focus on Ma Mary and Aunt Sarah's younger day 

It's the news we didn't know we needed.

The next episode of Derry Girls is set to be a flashback episode that will bring us back to when Ma Mary (Tara Lynne O'Neill) and Aunt Sarah (Kathy Kiera Clarke) were teenagers in the '70s.