He has threatened resignation on numerous occasions, but when David Davis did leave his post late last night it was shocking and unexpected.
It had appeared that peace - albeit a fragile peace - had broken out in the British Cabinet following Friday’s meeting during which a common Brexit negotiating strategy had been agreed.
But the divisions which were papered over could not withstand the weekend.
Michael Gove - who had played a central role in the Leave campaign - defended Theresa May’s plans yesterday in the face of mounting criticism from MPs who had wanted a more radical Brexit approach.
But it became the silence of others such as David Davis, which hinted at the uneasiness of the truce which had been agreed.
That silence was definitively broken with Mr Davis’s resignation, but the letter which accompanied his decision to stand down lays bare the deep divisions between him and the Prime Minister in recent months.
Mr Davis talks of the "significant number of occasions in the last year ... on which I have disagreed with the Number 10 policy line, ranging from accepting the Commission's sequencing of negotiations through to the language on Northern Ireland in the December Joint Report".
He described the fact that he was not willing to be a "reluctant conscript" to Theresa May’s plan on Brexit.
It was known that Mr Davis had been unhappy with Mrs May’s reliance on senior civil servant Olly Robbins.
Having left Mr Davis’s department and moved to Number 10 as Europe Advisor last year, Mr Robbins was a key player in the talks with Brussels.
David Davis and Olly Robbins did not share a vision of what Brexit should be, and Mr Davis is said to have become increasingly frustrated at what he considered a movement towards a "soft Brexit" being advocated by Mr Robbins.
Interestingly, Mr Davis’ resignation letter makes no mention of a pledge of loyalty or commitment to the Prime Minister.
It therefore leaves open the question of just what role the former Brexit Secretary plans to play from here.
Later today Theresa May will make a statement to the House of Commons.
It had been meant to be a chance to sell her Cabinet’s Friday proposal to MPs and the wider public. It will now be dominated by the ongoing political crisis.
This evening the Prime Minister is due to address a meeting of her backbench MPs. With many unhappy about Friday's plan, it was already expected to be heated and tense.
This has now heightened the stakes for that meeting as Theresa May tries to unify her wider party when it is clear unity has not been reached at Cabinet level.
The immediate questions now are - who might follow Mr Davis and will departures precipitate a leadership battle?
If it does, can a general election be far behind?
And what does all of that mean for Brexit - the most important political issue of the day - and one on which the clock is ticking?
Brexit has acted as a catalyst for fast moving political developments in the past.
With so much still uncertain on foot of Mr Davis’ resignation there is - once again - a sense that no one can really predict the chain of events which may develop from here.