Much to the delight of fans, Gavin & Stacey returned to screens last Christmas and referenced a mystery that has puzzled audiences for over a decade.
What happened on the fishing trip? Sadly, the special didn't confirm what actually happened on Jason and Bryn's now-legendary outing - but the comedy did tease a few more details.
With the sitcom's hit 2019 special returning to our screens for a primetime Christmas Eve repeat at 8:40pm on BBC One, here's a recap of everything we know so far - as well as a few of the weird and wonderful theories the internet has produced.
There's every chance we'll never find out, with some speculating that even series creators Ruth Jones and James Corden don't know, but we've investigated and put together several clues...
The original theory
The fishing trip became harder to decode as the series progressed, with the information from series one alone suggesting a fairly simple explanation.
At Gavin and Stacey's wedding reception, Jason met Bryn outside the venue and attempted to clear the air.
He said: "I never told anyone, you know. And besides, it wasn't a big deal. Lots of people do it, it's not against the law."
Bryn replies: "Jason please, how can I ever forget that look on your face?"
This short interaction suggests that perhaps Jason simply walked in on Bryn at a private moment, more than enough to cause serious awkwardness between an uncle and his nephew.
However, the information in series two complicates matters a lot...
"It defies gravity"
Towards the end of the second series, Bryn revealed to Jason that he told Dave Coaches what happened six months after the incident when he was feeling particularly low.
"Oh, why did I tell him every damn thing?" he asked.
To which Jason replied: "Even about--"
Bryn interrupted and shouted: "Yes, everything!
While Dave was "sickened by the whole thing," Jason reassured Bryn by pointing out that what happened is "perfectly legal in this country."
In the final episode of the series, Dave and Bryn have a moment alone as Nessa prepares to give birth.
The following interaction is arguably the most perplexing part of this entire case, as Dave has two lines that throw the original theory into disarray.
"You know what? I wish I didn't know either but I do," he said. "But it's difficult for me as well, seeing you standing there with a soup. It sets my mind racing, you know?
"Even if I wanted to tell anyone, I wouldn't know where to start because in my mind it's a physical impossibility. It defies gravity."
This clue seems to suggest that soup was involved in whatever happened on the trip. As for gravity-defying phenomena, for simplicity's sake it could be assumed that this is an exaggeration on Dave's part...
Jason was actively involved
The final nail for the original theory comes in the 2008 Christmas special, where a reconciled Bryn and Jason discuss Dave's knowledge of the incident.
Bryn said: "There's the occasional comment. The odd look. Times when I know that he's wondering how a man and his nephew could..."
Jason cut him off saying: "Yeah, yeah, I know."
When Dave walked in on the pair of them talking, Jason dressed only in his underwear, he looked visibly uncomfortable with the situation.
Bryn went on the defensive: "David, it is not what you think."
Dave replied: "Listen, it's none of my... you can do whatever you like."
These two exchanges suggest that whatever happened was something that both Bryn and Jason were actively involved in, rather than a mere accidental encounter.
"What happened was..."
It seems series creators Ruth Jones and James Corden know just how much viewers want full details of the fishing trip, and teased the entire nation with the 2019 Christmas special. When the topic of the troubling trip came up, it seems Bryn and Jason were finally ready to tell the whole family what really happened - only to be interrupted when the kids run in.
However, we did get a few more details - Bryn said: "It was very dark, in every sense of the word."
Jason replied: "And can I just point out that we knew nothing about camping."
When Jason begins to take responsibility for the incident, Bryn steps in claiming the blame belongs to him - again suggesting both were actively involved in the mysterious encounter.
So, what happened on the fishing trip?
It seems likely that somewhere between the end of the first series and the beginning of the second, Corden and Jones changed the fishing trip incident to confuse fans trying to figure out what happened.
Where the first series discusses it like an unfortunate mistake, later episodes allude to something that seems altogether more complex and disturbing.
Several fan theories present elaborate stories about Bryn and Jason stripping off and getting close to stay warm, but the incident could actually be something far less extreme.
Think about it: Bryn has lived a very sheltered life in Barry, often being amazed by the simplest of things ("is that what you would call a power shower?"), so conversely he could well be horrified by something that most people would find fairly innocuous.
Of course, that wouldn't explain why Dave and Jason are so traumatised as well, but it's a strong possibility nonetheless.
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After all, Gavin & Stacey is a series that devotes so much time to mundane scenes - eating fish and chips, ordering a curry and talking about oven gloves - that it would be in-keeping with the show's sense of humour if its one huge mystery is revealed to be something quite ordinary.
It's so easy to imagine the disappointing truth finally being revealed, only for Pam to shout: "IS THAT IT?"