Guto Bebb was at the Farnborough Air Show when the career-changing text came through on his phone.
"I certainly didn't intend to resign," the now former defence minister said 24 hours later. "I didn't want to resign."
But quit he did and in his first interview since - with my BBC Wales colleague Elliw Gwawr - he explained why. Members of the Brexit-supporting European Research Group may want to look away now.
The catalyst for his resignation was the government's decision to accept four amendments to its customs bill from the ERG, led by Jacob Rees-Mogg. Some, but not the prime minister, say the amendments kill the Chequers agreement. Guto Bebb saw them as "wrecking amendments".
The Aberconwy MP said: "The ERG group are a hard Brexit group within the Conservative Party who are ideologically of the view that we have to leave with absolutely no further trading relationship with the EU which I find quite disturbing because that would damage our agricultural sector, our manufacturing sector in Wales and I think that's an important consideration for any politician.
"So I pushed back, I spoke to the whips. I was in constant communication with my whip all day, highlighting the fact that whilst possibly I could accept two of the four amendments, there were two of the amendments which I thought were wrecking amendments with a simple intention of damaging the Chequers agreement which was formed by the prime minister and the cabinet."
He explained how he took the decision to resign. "When the government were not willing to compromise on this issue I felt I had no choice because ultimately I wanted to send the prime minister to talk to the European Commission, to talk to the European Commission from a position of strength with the party united behind her.
"I think the ERG amendments yesterday have absolutely undermined the negotiating position that the prime minister had and I felt duty bound to try and vote to highlight the fact that the Conservative Party should be led by the prime minister not by the leadership of the ERG group."
He added: "I voted last night to support the prime minister's position, or certainly the prime minister's position at two o'clock, so to find myself in a situation where I'm now seen as someone who's rebelled against the government I find quite bizarre. the rebellion yesterday came from the ERG group.
"The result of yesterday from a political point of view is that there are question marks now over who exactly does lead the Conservative party."
Mr Bebb said he supports the prime minister and praised her "sense of duty" but yesterday's decision to give in to the ERG was "a significant mistake on the part of the government".
He added: "The Conservative Party needs to ask itself some serious questions. I never thought when I joined the Conservative Party that I was joining a party that was ideologically unbending. I thought it was a pragmatic party which would always try and do the best thing and would always look to do the best thing for the economy of the United Kingdom.
"I believe very strongly that we need a free market economy that works for Wales and the United Kingdom and I'm just of the view that there are some now within the party who are more intent on this concept of ideological purity on a Brexit which most people didn't vote for. Most people voted to leave the European Union, not for a termination of our relationship with the European Union.
"And I am very concerned as to the future of the party when we have that type of ideological position being pushed forward to the extent that it is being pushed forward by the ERG group."