Jonathan Arnott has resigned as UKIP General Secretary and constitutional Affairs spokesperson.
The former school teacher who's been a North East Member of European Parliament since 2014, released a statement following the party's dismal general election performance.
He said: "I have remained with UKIP through the good times and the bad, when the Party was polling less than 1% in 2007."
Within his resignation letter, Arnott spoke of his loyalty towards UKIP leader Paul Nuttall, a personal friend who'd been "badly let down".
Earlier today, Nuttall resigned as UKIP leader after the party failed to gain a single seat in Westminster.
Nuttall said: "I'm standing down today as the leader of UKIP with immediate effect. This will allow the party to have a new leader in place by the conference in September."
Jonathan Arnott praised his party leader in his resignation letter: "He has done a good job in the most difficult of circumstances and out of loyalty to the many hard-working UKIP candidates up and down the country, I remained silent during an General Election campaign with which I profoundly disagreed. I can no longer remain silent now."
Arnott described the party as having "lost its way in recent times" and he could not "in all conscience support and propagate the policies that were being articulated."
He added: "It would be improper for the General Secretary of the Party to be as blunt as I need to be or even to say what I have said in this statement. My position is therefore untenable and I must therefore resign as General Secretary and Constitutional Affairs spokesman. I have agreed with the party that this will not take effect until after the emergency NEC meeting on Monday.
Jonathan Arnott's full resignation letter can be seen here on his website.