In hindsight, we should have spotted it earlier.
Perhaps it was planned all along but after hints and rumour, last month we heard for definite that it's game on.
The 'game' is a 12-hole match between the duo at the Wynn Golf Club in Las Vegas.
As for the 'on', that'll be Friday, November 26, the day after Thanksgiving.
Expect the phony war to be ramped up as the day approaches.
The Match - A Brief History
This is the fifth edition of the event but the first since the initial head-to-head showdown between Tiger Woods and Phil Mickelson in 2018.
2018 - Phil Mickelson beat Tiger at the 22nd hole - Shadow Creek, Las Vegas
2020 - Tiger Woods & Peyton Manning beat Phil Mickelson and Tom Brady 1up - Medalist GC, Florida
2020 - Phil Mickelson & Charles Barkley beat Steph Curry and Peyton Manning 4 and 3 - Stone Canyon GC, Arizona
2021 - Bryson DeChambeau and Aaron Rodgers beat Phil Mickelson and Tom Brady 3 and 2 - The Reserve at Moonlight Basin, Montana
Tale Of The Tape
A look at the career achievements of the two rivals:
World ranking: 16
Major wins: 4
PGA Tour wins: 8
European Tour wins: 6
World ranking: 7
Major wins: 1
PGA Tour wins: 8
European Tour wins: 2
Recent Form and Nevada Form
A look at how the pair have fared recently and in past events in Las Vegas or Nevada as a whole:
MC Houston Open
MC World Wide Technology Championship at Mayakoba
38th CJ Cup
67th Shriners Children's Open
2pts from 4 matches at the Ryder Cup. Won Singles 2&1 (v Bernd Wiesberger)
2.5pts from 3 matches at the Ryder Cup. Won Singles 3&2 (v Sergio Garcia)
11th Tour Championship
2nd BMW Championship
31st The Northern Trust
Record when playing head-to-head
Who knows, perhaps this could be the decisive factor.
If they really do get up each other's noses, that will come out most when actually playing together.
Koepka has accused DeChambeau of slow play so will that knock Brooks out of rhythm?
Or will Koepka's (perhaps genuine) ice-cool and withering contempt of his rival get to DeChambeau?
There isn't actually too much evidence as they've only played four competitive rounds together.
2019 Arnold Palmer Invitational R2: DeChambeau 70, Koepka 73
2019 Arnold Palmer Invitational R1: DeChambeau 75, Koepka 74
2018 Tour Championship R3: Dechambeau 66, Koepka 67
2016 Masters R4: DeChambeau 72, Koepka 72
DeChambeau has shot lower twice
Koepka has shot lower once
Quickest on the draw
With the contest over just 12 holes, let's check some relevant scoring averages.
2021 R1 Scoring Average
70.19 Bryson DeChambeau,70.20 Brooks Koepka
2021 First 9 Scoring Average
34.59 Bryson DeChambeau34.86 Brooks Koepka