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. 

Lisa McGee, the creator behind the hit Channel 4 sitcom, told Digital Spy she always wanted to write something based on the two sisters, and the final series was her "last chance" to do so.

"[The flashback episode] was the first episode of this series I pitched to Channel 4," she added.

"It's risky because it's very different, and it's not the show's formula, but they just went 'Yeah, go for it' because they're Channel 4 and they are incredible and taking risks is the thing they're known for."

Shauna Higgins will play the young Mary, while Dearbhaile McKinney will play Sarah's younger version.

Shauna Higgins will portray the younger Mary in episode 5, while Dearbhaile McKinney will star as teenage Sarah.

Speaking about Ma Mary and Aunt Sarah, McGee said "before shit got serious and they had their family, they were the silly people too."

"I mean, they're still quite silly on the show as adults, but you know, all mummies were young once."

Speaking to the outlet, McGee said the fifth episode of the final series will give an insight into the "horrific" times Ma Mary and Aunt Sarah grew up in.

"For the parents' generation, it was a war zone. It was horrific what they went through, and we just didn't appreciate it."

Writer Lisa McGee in front of a Derry Girls mural.

The Derry Girls writer said writing the series has been a "real learning experience" for her as a person, not just a writer.

"We just moaned and then complained when we were not allowed to do anything. By writing the show and looking back I realised why they were so strict, why the school was so strict, what they had seen, what they lived through, and I have such an appreciation and respect. I'm so embarrassed at how we behaved now." 

Alongside the flashback, it was also recently confirmed that the series will conclude with a special 45-minute extended episode set during the Good Friday Agreement.