Derry Girls viewers raced to Twitter on Wednesday night, as the final episode aired on Channel 4.
But a surprise cameo, linked to a past series of the show, left viewers stunned and "mind blown" in the final moments of the hit show.
Chelsea Clinton, the daughter of former US president Bill Clinton, made an appearance from New York in the final scenes, after receiving a letter.
While the show was set in the 1990s, the closing moments took place in present day - 27 years after Clinton’s momentous visit to Derry.
A mystery woman was seen receiving a letter in the mail, with it confirmed to have got lost on its way to her in the 90s.
Chelsea was then shown on screen, as she read the letter out in its entirety - written by the show's lead characters.
The group had sent Chelsea the letter during the series two finale, and in the closing scene it finally made its way into the hands of the intended person.
Viewers couldn't cope with the cameo, stunned that the show had managed to convince the writer and global health advocate to make an appearance.
Not only that, but they couldn't believe the group's letter had finally been revisited and landed in its planned destination - even if it was decades later.
Taking to Twitter, one fan said: "CHELSEA BLOODY CLINTON LADSSSS I CANT COPEEE."
Another tweeted: "Chelsea Clinton my mind's blown," as a third added: "How the f**k did #DerryGirls get Chelsea Clinton?????"
A fourth viewer wrote: "The power derry girls has to get a literal Chelsea Clinton cameo to close out the series…this show is truly unmatched."
Speaking of the guest appearance, Chelsea said: "Thanks to Lisa McGee’s incredible talent, and that of the wonderful cast and crew of Derry Girls, people around the world have been able to better understand and relate to a hugely significant and important period of history in Northern Ireland and for the world.
"Like many, I am a big fan of the series, and I was honoured to be able to appear in the very special final episode. I hope people enjoy watching it as much as I enjoyed being a part of it!"
Chelsea wasn't the only cameo during the episode that had viewers squealing with excitement.
Fans were loving the appearance of Irish comedian and actor Ardal O'Hanlon too.
"OMG, Ardal O'Hanlon?? So many great cameos in this season," said one viewer.
A second fan said: "Ardal O'Hanlon i love you <3," as a third wrote: "ARDAL ON DERRY GIRLS."
Liam Neeson also made another cameo for the final episode, after previously appearing on the show.
Derry Girls is now available to watch in full on All4.
