It was truly a gobsmacker.
Rafa Benitez's much-talked about betrayal of the Anfield faithful when he became Everton manager doesn't even come close.
A more appropriate comparison would have been Sir Alex Ferguson travelling up the M62 from Manchester to take his place in the Liverpool dugout.
When word came through just after 19:30 BST on Monday evening that Mickey Harte had stepped down as manager of the Louth footballers to apparently become Derry boss, many of us thought it was an April Fool that had somehow got stuck in cyberspace for five-and-a-half months before arriving to tickle us.
But truth indeed is occasionally stranger than fiction and it soon become clear that this was seemingly for real, whatever about us having to wait for Tuesday night's official confirmation by the Derry GAA's county committee of the appointment of Harte, 71, and his faithful assistant Gavin Devlin.
However, the mind continued to race in a myriad of directions when attempting to take in the astonishing news.
How could Harte agree to manage the old enemy?
How could a man who remains the very embodiment of Tyrone GAA for many of us, even though he was reluctantly pushed out of the Red Hand manager's job three years ago, even consider taking charge of the old enemy?
And make no mistake, while the All-Ireland winning exploits of Harte's Tyrone and Joe Kernan's Armagh in the noughties fostered an intense rivalry between the two counties, the Red Hand County's relationship with Derry remains the gold standard when it comes to Ulster GAA enmities. The original and the best.
As ever, Oak Leaf county 1993 All-Ireland winner Joe Brolly was fast out of the traps in reacting to Harte's impending arrival with his social media posts including the assertion that it was the "worst thing to happen to Derry since the plantation".
In a later interview with BBC Radio Ulster's Talkback, Brolly told William Crawley: "I'll not be going to any [more] Derry senior games", adding that it was the "last straw in relation to Derry senior football".
The reaction from elements within the Red Hand County was just as voluble with Owen Mulligan, who played in Harte's three Tyrone All-Ireland winning teams of the noughties, uttering: "May as well have joined Rangers".
But while the reactions were loud and wonderfully entertaining, we then somehow had to pivot forward to the practicalities of it all.
Harte set to renew hostilities with McGuinness
Can you imagine traffic gridlock around Healy Park or Celtic Park next spring when the expectant throngs turn up to see Mickey Harte taking his place on the Derry (I nearly wrote Tyrone there) bench for the Division One tussle between already sworn enemies? That game will surely have to be all-ticket.
Of course, the vast majority will be rightfully respectful to a truly great GAA man who, we must never forget, tragically endured the loss of his beloved daughter Michaela in 2011.
But no doubt a few Tyrone folk are musing over what jeers they may direct at the new 'Derry' manager as he makes his way to shake hands with Feargal Logan and Brian Dooher before taking his place in the Oak Leafers' dugout.
With Jim McGuinness returning in Donegal, it's almost a case of 'back to the future' with the Glenties man out to maintain his championship Indian sign over Harte's red and whites - now of the Derry variety - a decade on.
The competitor in Harte
The question remains of course remains why did he do it?
The cynics out there will spout in bottom line terms but I would contend it is the fierce competitor in Mickey Harte that made this opportunity of taking on a team capable of scaling the All-Ireland summit simply irresistible.
Let's not forget, Derry should have beaten Kerry in this year's All-Ireland semi-final - even in spite of David Clifford's heroics - and with two successive Ulster titles banked, Harte will firmly believe that he can guide them to Sam Maguire Cup glory.
The Tyrone legend performed near miracles in guiding Louth from Division Four to Division Two during his three seasons in charge and indeed they had a shot at going all the way to Division One when they faced Dublin in effectively a promotion play-off last March.
But the Dubs proved too strong as they won by seven and the margin between the same two teams was a massive 21 points seven weeks later in the Leinster Final.
Despite his side's narrow defeats by Cork and Mayo during the group stages of the All-Ireland Championship, another 28-point thumping by Kerry may have finally induced the realisation - even in a man as positive as Mickey Harte - that Louth had reached their ceiling.
Yet up until Monday evening, there was no inkling in the GAA world that Harte was in the frame for the Derry job, with him seemingly committed to the Wee County until 2025, as Malachy O'Rourke appeared the obvious candidate to take over following Ciaran Meenagh's departure last week.
But one social media post by Louth GAA changed all that and nearly 24 hours on, we are still trying to come to terms with the shock.