It was the decisive moment of the Wales-Scotland match and it all hinged on a crucial conversation between referee Nic Berry and his TMO Brett Cronan.
With 67 minutes on the clock at the Principality Stadium, the sides were tied at 17-17 in what was a real cliff-hanger of a contest.
After Welsh skipper Dan Biggar had struck the woodwork with a long range penalty attempt, the home side regathered the ball, with Alex Cuthbert going for the try in the corner.
The TMO check on whether the winger had scored or not was to have crucial consequences.
Speaking to his countryman Cronan, Aussie ref Berry said: “On-field decision is a try, we have got a grounding, we just need to check touch.
“If not, we are going to come back because I was playing advantage for a knock-on from blue.”
That was a reference to Scotland fly-half Finn Russell having stuck out a hand to block a pass from Tomos Williams which was aimed at prop Dillon Lewis in the build-up to Cuthbert going over.
So, clearly, in Berry’s mind it was either going to be a try or a scrum for Wales.
After checking the replay of Cuthbert’s effort, Cronan said: “The player has clearly put his foot into touch.”
But he then critically adds: “So you need to go back for your penalty.”
Berry reacts to this by saying: “It’s not a penalty mate, I just had it as a knock on. Do we need to have a look at it?”
Cronan replies: “Sorry, we’ll check that now for you.”
Commentating for the BBC, World Cup final referee Nigel Owens immediately recognised the significance of what had been said.
“The TMO has just triggered something in the referee’s mind now,” said Owens.
“Was that knock-on deliberate or not?
“They will look at Finn Russell’s actions. Was he trying to make a genuine attempt to catch the ball and was he in a realistic position to do so? This is interesting.”
The wheels were now in motion and the outcome was to be oh so telling.
Adding his thoughts on commentary, former Wales and Lions skipper Sam Warburton said: “History has told us one hand, which is what Finn Russell does, tends to suggest its a penalty.”
After watching a replay of the incident, referee Berry delivered his verdict.
“He’s only stuck the one hand out and he’s knocked the ball forward,” said the Brisbane-born official.
“He’s chanced his luck and it hasn’t gone.
“He’s not in a position to re-gather that.
“We have got a deliberate knock forward by blue.
“Because of the vicinity to the goal-line, it’s going to be a penalty and a yellow card.”
So it was off to the bin for Russell.
It meant rather than facing a five-metre scrum with 15 men, Scotland were now facing a penalty while down to 14.
And that was all sparked by the words used by the TMO in his vital intervention.
Whether it was a slip of the tongue by Cronan or a presumption on his part that Berry had been signalling a penalty when he put his hand out for advantage, it’s hard to say.
But it was absolutely crucial.
Wales kicked to the corner and from the resulting attacking passage, Dan Biggar landed the drop goal that was to prove the winning score in a nail-biting 20-17 triumph.
The Russell incident was discussed further after the game during the BBC coverage.
Dual code great Jonathan Davies commented: “That’s a yellow card for me. He leads with one hand.”
Former Scotland skipper John Barclay added: “I don’t know what he’s doing.”
And England’s World Cup winning captain Martin Johnson said: “The ball is there and under pressure you put your hand in the cookie jar.”
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