*Warning – contains full spoilers for all eight episodes of The Diplomat season 4.*

The fourth season of The Diplomat proved to be another rollercoaster ride for Keri Russell's Kate, who attempted to keep both her marriage to Hal, and the alliance between the US and the UK, together.

It proved to be a particularly tricky task this time around, as President Grace Penn's behaviour became more aggressive and difficult to predict, following a failed assassination attempt in the first episode.

The season also saw resignations, firings and deaths, with the show's chess board getting moved around in some truly significant ways. But just how did it all come to an end, and where have we left the show's central players heading into a potential season 5?

Read on for everything you need to know about the ending of The Diplomat season 4.

The Diplomat ending explained: What happened to Austin Dennison?

Fans may have noticed that, in the first couple of episodes of The Diplomat season 4, Austin Dennison was conspicuously absent.

This is because, as was revealed at the end of episode 3, he had been sent on a visit to Amritsar by Prime Minister Nicol Trowbridge, one from which he never returned.

That's right, in tragic circumstances right after he got married, Austin Dennison was killed in a helicopter accident while on the trip.

This led Trowbridge to spiral, and ultimately conspired with other events to bring about his political downfall.

Why did Nicol Trowbridge resign as Prime Minister?

At the end of The Diplomat season 4 episode 4, having spent the entire instalment imagining the late Margaret Roylin talking to him, Nicol Trowrbridge resigned as Prime Minister.

Ultimately, this appears to have been brought about by Kate, who in her final meeting with him, made both the Prime Minister and new Foreign Secretary Robyn Palmer aware that she had a sensitive recording.

This recording revealed that, after he found out about Roylin's involvement in the HMS Courageous bombing, he had throttled her, in what appeared to be an attempt to kill her.

Kate brought this up on Hal's advice, as a method of attempting to control the Prime Minister, who now knew that the American's had stolen the Poseidon from British waters.

Instead, recognising the predicament he was in, and perhaps with a push from Palmer, Trowbridge resigned his post, and was replaced, following an internal leadership campaign, by Bethan Vaughan.

What happened to Stuart?

As the fourth season of The Diplomat came towards its end, the ever-upstanding Stuart found out that the attack of the HMS Courageous had actually been part of a plan laid in motion by Grace, rather than former President Rayburn, as he had been led to believe.

Along with her erratic behaviour and threats to send warships into British waters, this was a step too far from him. Stuart posted a message on the State Department Descent Channel, an action which was mocked by Billie and Eidra as inconsequential. However, it proved to be anything but.

A furious Grace, who felt her authority being challenged from all angles, decided to move Stuart from his posting in London, and it was suggested that while he wasn't officially being fired, he wouldn't be getting another one.

This was deemed to be a violation of the Foreign Service Act and the First Amendment, but the ever-practical Eidra simply stepped into motion, collecting his things from London and planning their next moves. Stuart was crestfallen, but Kate advised him against any action against Grace which would land him in legal hot water.

What happened at the G7?

While at the G7, Kate, Hal, Todd, Billie and Miguel Ganon all expressed their fears that, since she was nearly assassinated in the season premiere, Grace had become more erratic, with a higher threshold for the lives of civilians and servicemen that she was willing to risk.

She had also started threatening the UK. The new Prime Minister, Bethan Vaughan, had told the Russians that they could come and collect their dead from the submarine which had been grounded in British waters, even though she was aware this meant they would find out the Americans had stolen their weapon, the Poseidon.

Kate had tried to keep the peace, but Grace had made it clear that she would send warships into US waters to turn the Russians back if the British failed to do so themselves. This could ultimately threaten both the US and UK alliance, but also risk provoking war with Russia.

As the G7 got underway, Grace pre-empted a statement from the British Prime Minister by telling the council members about the situation, and made an implicit threat that if this wasn't followed through, or if the British government moved to have the US removed from the G7, then the forum itself would be done for. In the process, she insulted all of the other countries present.

Not willing to stand for any more of Grace's behaviour, Kate stood up in front of the entire forum, and resigned her post as the ambassador to the UK, saying she could no longer work for, support or defend the Penn administration. With that she left the building, having told Hal to stay in his role as Vice President and say he knew nothing about her decision ahead of time.

Following this, in an unexpected move, Billie followed suit, resigning publicly from her role and rescinding her support of the administration. She was then followed by Miguel, meaning the administration had lost its UK ambassador, White House Chief of Staff and Secretary of State in one fell swoop.

As the trio headed towards the gates of the location in Italy where the G7 was being held, the doors surprisingly opened once more behind them, with Hal following out. It appeared he had followed the trio in their footsteps, although it seems likely that his resignation wouldn't take effect as immediately as that of the others.

As the four of them came together in front of the assembled press, Kate announced that Hal, as Vice President would be making a statement - at which point the credits rolled, and fans across the globe were left amazed by what they just witnessed, and desperate to find out what happens next.

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