I was there, and you get a feeling in someone's presence whether they know something, but nothing about Ten Hag's demeanour suggested that he was aware of what could be about to come his way.
"In football not always the best team is winning," Ten Hag started during his post-match press conference, and he was right; Man United deserved to beat West Ham - they should have been out of sight at the interval, with Alejandro Garnacho (twice), Bruno Fernandes, Marcus Rashford, Rasmus Hojlund and Diogo Dalot all passing up huge chances - the football was better, the result was not.
An incredibly soft West Ham penalty ultimately decided the contest, and it proved to be the final straw for new minority shareholder Sir Jim Ratcliffe and his newly-assembled football department, with senior figures at Old Trafford deciding that Ten Hag could not continue.
"We are grateful to Erik for everything he has done during his time with us and wish him well for the future," read part of Man United's statement, with Ten Hag departing having won two domestic trophies in two seasons in the shape of the EFL Cup and FA Cup.
Man United were eighth in the Premier League last term, though, some 31 points off the champions Manchester City, losing 14 of their 38 matches, with Ten Hag's job largely being saved due to his FA Cup success over Man City.
Man United sacked Ten Hag as manager on Monday
The Dutchman extended his contract at Old Trafford until June 2026 at the start of July, but there has simply not been enough this season to suggest that Man United are heading in the right direction under his leadership.
Three straight draws in the Europa League to FC Twente, Porto and Fenerbahce have left them in 21st spot in the Europa League table, while they sit down in 14th spot in the Premier League table, boasting only 11 points from nine matches.
Only Crystal Palace (six) and Southampton (six) have netted fewer goals than Man United (eight) in the Premier League this term, while they have been beaten 3-0 by both Liverpool and Tottenham Hotspur at Old Trafford in 2024-25.
Ex-Man United captain Gary Neville hit the nail on the head on Sunday when he said that "anybody that's half decent" are capable of beating the Red Devils, and INEOS have ultimately now decided that enough is enough.
Ten Hag was backed over the summer, with Joshua Zirkzee, Leny Yoro, Matthijs de Ligt, Noussair Mazraoui and Manuel Ugarte brought in, but the team continued to lack identity, and the Red Devils have gone backwards since a very encouraging first season under the Dutchman, which saw them finish third and win the EFL Cup.
Man United considered replacing Ten Hag over the summer
Man United spoke to other managers in the lead-up to the FA Cup final last season, with Thomas Tuchel among those in discussions with the club, but an agreement with the German could not be reached.
Tuchel has now accepted the England job, with the Three Lions clearly sensing that this was coming, and the Football Association wanted to ensure that they struck a deal before Man United had the chance to make an expected move for the German.
According to BBC Sport, the decision to replace Ten Hag was 'unanimous', but it is ironic that the change has come after an encouraging performance at West Ham, where the football was a lot better than the majority of what has been served up this season.
Ten Hag simply did not react to West Ham's game-changing substitution of Crysencio Summerville, though, and it was incredibly controversial that Ugarte did not feature at the London Stadium after putting in a brilliant performance for the Red Devils in their Europa League contest with Fenerbahce last week.
Man United fans are incredibly loyal, and it says a lot about the supporters that many were still willing to give Ten Hag the benefit of the doubt, but even the most ardent of supporters were starting to find it difficult.
In short, Ten Hag had run out of chances; there were too many bizarre tactical calls during matches, too many bad performances. Enough had become enough - he was trying, but the more things change, the more they stay the same.
Amorim emerges as clear favourite to replace Ten Hag
Ruud van Nistelrooy has been placed in temporary charge of the Red Devils and will lead the team into Wednesday's EFL Cup fixture with Leicester City, but a permanent replacement for Ten Hag could soon be appointed.
Indeed, it is understood that Sporting Lisbon head coach Ruben Amorim has verbally agreed to become Man United's next manager, with journalist Ben Jacobs claiming that the two clubs are now working on a compensation package.
As called by journalist David Ornstein, the composition fee for 39-year-old Amorim, who is regarded as one of the most outstanding young managers in European football, is €10m (£8.3m).
Man United will welcome Chelsea to Old Trafford in the Premier League on Sunday afternoon, and it would not be a shock to see the home side put in a brilliant performance and pick up all three points.
There remain plenty of issues in the squad, and there have again been injury problems this season, but the players have again underperformed, and only Ten Hag will know whether he got everything available out of the current group.
Were Man United right to sack Ten Hag?
Man United have spent over £616m since Ten Hag's arrival as head coach, and "identity" has been a word used on numerous occasions when discussing the Dutchman's time at the club.
"The lack of identity and style is something that has been a mystery for the last two-and-a-half seasons. The recruitment has been awful at times but I believe there are a group of players who can play better than they are," Neville told Sky Sports News.
"Lack of style has been the biggest problem. It is a real struggle watching them play and it hasn't changed in the last 18 months. That has been as bad as the results. No-one watches United and doesn't think the players are better than what they are showing.
"I thought it was coming. Looking at that Tottenham game a few weeks ago I felt I had seen this before. It was a bad day for Manchester United and a bad day for Erik ten Hag. Overall, the challenges of the results and performances have meant that the owners have decided to sack him. I don't think anybody will be truly shocked."
In truth, this was coming sooner or later, with Ten Hag only ever one result away from a disaster, and that is simply not sustainable.
The 54-year-old can leave with his head held high, and a healthy pay-off in the region of £16m, and it would not be a shock to see him return to management in the near future and enjoy more success in terms of trophies, but he was never going to be a long-term Man United manager, and the Red Devils must now look to the future.