Derry Girls' writer Lisa McGee on how success turned tears into smiles in a City of 'Troubles'

But this is Derry, where everybody knows everybody and anything can happen.

Writer Lisa McGee, a vibrant Derry girl original herself in a standout red tartan coat, sparks a hubbub of excitement among locals when they spot her, but she can't linger - she has a red carpet premiere to attend, followed by a Derry Girls private party at the Guildhall.

As excitement builds for the launch of the third and final season of the worldwide hit show, which will begin on Tuesday, there is little talk of anything else on the streets of this remarkably friendly walled city.

The people here have welcomed Derry Girls with open arms as encapsulating its true mettle and resilience despite the pains it has endured.

McGee had no idea how successful her show would turn out to be, telling the Herald she thinks it will only be when the final series is broadcast that it will dawn on her.

"I just hoped enough people would watch it that we would get a second go at it," she said.

"It still hasn't really hit me. When it's all over in the finale, I'll go, 'Oh God, that was mad'. It was never the plan (to be a massive success), and I think if it had been the plan it wouldn't have happened."

Before McGee arrived at the mural, two older women were taking selfies there.

"My favourite bit is the way they say we keep our toasters in the cupboard," said one, in reference to the Catholic versus Protestant blackboard. Her friend added in hushed tones: "We didn't know any nuns, though."

Before them were two older Northern men, looking sheepish as they too posed in front of the mural.

"My daughter will kill me if I don't," one said.

What Derry Girls means to Derry people is almost beyond words.

They appreciate how normal and warm the lives of the families are depicted against the most troubling circumstances that took place around them, said guide Garbhan Kerr, who runs a tailored Derry Girls tour during the summer months.

"Lisa is telling you what happens in your house, but you don't tell anybody," he said.

He believes a simple reason behind the worldwide success of the show is the ability on Netflix to turn on subtitles.

"The tourists tell me they need the subtitles because the lingo here and the slagging is very unique," Mr Kerr said.

He once led his group up Pump Street, where the show's fictional bakery is set.

Brandishing one of the famous cream horn pastries bought elsewhere, he was complaining that they don't fill the cream all the way to the bottom when an old lady passing by chipped in, saying: "You're going to the wrong bakery."

"The group absolutely loved that," Mr Kerr said.

At the Guildhall, women from Creggan Enterprises' Unheard Voices programme - which aims to mobilise marginalised women to build sustainable peace and prosperity - had gathered to meet the mayor. All identified as genuine Derry girls and are big fans of the show.

"It came just at the time when the city needed something more," Ruby McNaughton said. "It's put us on the map."

"I love it," Sharon Austin added. "All the slagging - that's us.

"Our wee city gets overlooked because for tourists it used to be all about the walls and the Troubles. This is something more positive. This is about the people of Derry and who we really are."

City mayor Graham Warke, of the DUP, said "bus after bus" of American tourists have visited Derry in the past three weeks.

"It's priceless what it has done for us," he said. "It's helped our economy when economies are down. It's opened everything up.

"What a show it is - it's absolutely brilliant. It brings out the best in everybody in this city."

With the show ending after this third series, there is some urgency about how to build a lasting legacy.

"It's something we're looking into," said Karen Henderson of Visit Derry, the city's tourism promotion organisation.

Officials from Tourism Ireland and Britain were coming in to discuss the marketing potential, with Derry Girls products such as branded beers from the Walled City Brewery - the "Sister Michael" is a coconut stout, while "the Wee English Fella" is immortalised in a strawberry pale ale. "Sexy Priest" was discontinued.

Back at the mural, retired publican Hugh McDaid, of Badger's Bar, told how he has never regretted giving his approval for it to be painted on the gable end of his property three years ago.

"All ages come to it and all ages watch it," said the firm fan of the show.