The Diplomat season 4 ending explained: Breaking down Kate's bold move and that final cliff-hanger

Warning: Spoilers ahead for all episodes of The Diplomat season 4.

Another thrilling instalment of The Diplomat has come to an end, and as is customary with the hit political thriller, there's a huge amount to unpack after that season 4 finale.

This season opened with Kate reeling from the discovery that the catastrophically dangerous nuclear-powered weapon the Poseidon, hadn't been buried in cement at her request at all, but actually stolen by Grace and Hal.

By the time the credits rolled on episode 8, there'd been a shocking death, several resignations, and a growing number of couples re-thinking whether or not their romantic entanglements should continue.

Let's break down what happened.

The Diplomat season 4 ending explained

In the build-up to the finale, Austin Dennison was nowhere to be seen. By episode 3, it came to light that Prime Minister Nicol Trowbridge had sent him on a visit to Amritsar, India, to meet with the country's foreign minister.

Sadly, he didn't make it back as he died in an unseen helicopter crash that happened off screen.

Austin's death pushed Trowbridge into a downward spiral that included him having visions of his deceased former adviser, Margaret Roylin and kicked off the start of what was ultimately his political downfall.

By episode 4, Trowbridge had resigned. He was a broken man after the troubling hallucinations of Margaret, and having been blackmailed by Kate - she made it clear to both the Prime Minister and Foreign Secretary Robyn Palmer that she had evidence of Trowbridge's wrongdoing.

This came in the form of a recording of the Prime Minister throttling Margaret after he found out about the part she played in the HMS Courageous bombing disaster. Upon resignation, Trowbridge is replaced with Jodie Whittaker as Bethan Vaughn.

During this season, Stuart found out the truth behind the HMS Courageous attack. Like most people, he believed President Rayburn had been responsible for the bombing, and is shocked to find out Grace was really the leading force behind it.

With Grace's growing confidence leading to risky behaviour and decision making, Stuart posted a message on the State Department Dissent Channel - an internal communications system that lets employees express confidential disagreements - to raise concerns about her.

When Grace found out, she removed Stuart from his London posting and it appeared he was going to be left jobless. With Stuart returning to Washington, Eidra would be staying in London - not only is Stuart probably unemployed, but it looks like his relationship could also be over.

During the finale's G7 summit, our leading characters, Grace, Hal, Kate, Billie, and Vaughn are all in the same room in Tuscany.

Grace unexpectedly kicks things off by announcing that Vaughn intends to let Russians into UK waters. The president says, "Americans are prepared to fire on any country that interferes with our mission."

She adds, "Nothing will stop us from keeping Russian warships and surveillance vessels and tactical weaponry out of the European seas." It's an outright threat, essentially saying that America will be doing whatever they want from now on, and nobody can stop them.

Immediately, Kate stands up, takes off her lanyard, and resigns to the President's face. Walking from the room, she's followed by Billie and Ganon who both want to follow her lead and make a stand against American tactics.

Grace is once again left furious and alone, but still intends to simply keep going with her mission to maintain absolute geopolitical control. While it initially doesn't look like Hal will join the walk out, there's sighs of relief all round when he eventually does.

For most of the cast and crew, Hal’s appearance with the rest of those walking out came as a surprise, as it was a detail kept secret until the filming of those scenes actually took place.

"In the read-through, that last page was redacted," Hal actor Rufus Sewell tells Tudum, sharing that his character's actions earned him "a round of applause that day" when the cast all found out the Vice President was doing the right thing.

However, the actor isn't sure his character made the decision because it was the noble thing to do - he thinks it could be down to Hal wanting revenge for the President earlier humiliating him.

Having already tried to stand up during the summit to express his feelings, he'd been "sat down" by Grace and left red faced. "It’s painful to play that because it’s not a good look," Rufus says of how Hal would've felt in that moment.

But, Hal is out, and now there needs to be a press conference. Without warning him, Kate informs the waiting reporters that her husband has something to say.

Stepping up to the mic, Hal goes to make a speech but viewers infuriatingly don't get to hear it, as that's where the finale ends.

Whatever his master plan, we won't get to find out what it is until season 5 - whenever that might be.

All 4 seasons of The Diplomat are currently streaming on Netflix.