The Diplomat season 3 ends with a twist that rocks its very foundation: What it means for season 4

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The Diplomat season 3 finale spoilers follow.

Being the US ambassador to the UK is a challenging job, as shown in the first two seasons of the show *The Diplomat*. Now, with her husband Hal Wyler becoming Vice President, Kate Wyler is also taking on the responsibilities of Second Lady, effectively balancing two demanding roles.

Throughout the later episodes of season three, she’s caught in a complex situation, juggling a relationship with Aidan Turner’s character, Callum Ellis, while maintaining the appearance of a happy marriage to Hal. Adding to the drama, relations between the UK and US have become strained due to the questionable actions of President Grace Penn, which were revealed last season.

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Because of this, British Prime Minister Nicol Trowbridge is now taking a hard line with the United States. This is happening despite the discovery of a sunken submarine near Britain, which is believed to contain a powerful, almost legendary nuclear weapon called Poseidon.

But nothing compares to the dramatic confrontation between Kate and Hal in the season finale. Just when you thought things couldn’t get more intense after the nuclear crisis, a shocking twist emerges that completely changes everything about the show, *The Diplomat*.

The Diplomat season 3’s ending explained

The third season ends with Kate and Hal arguing, but their disagreement is just the beginning of bigger problems.

Hal is struggling with the fact that Kate is now seeing Callum, especially since they’re currently separated. Meanwhile, President Penn was about to become intimate with her husband, Todd, when security unexpectedly interrupted them, concerned by the noises they were making.

Todd notices Grace isn’t as cheerful since becoming President, unless she’s with Hal. It turns out the First Gentleman is jealous of his wife’s Vice President, and this tension sets up the episode’s ending—though not in the way you might expect.

Kate and Callum find themselves unexpectedly sharing space, fully clothed. Callum jokes, “The fact that I can’t even touch you is agonizing.”

A major meeting begins between the US and UK. Penn offers assistance in recovering Poseidon and the submarine, but Trowbridge immediately rejects her offer and leaves.

Trowbridge suspects she’s not telling the truth, especially since he recently discovered the US government wasn’t honest about what happened with the aircraft carrier last season. Kate admits, “We have no credibility.”

UK Foreign Secretary Austin Dennison recently introduced his new wife, Thema Asiedu-Dennison, whom he married just months after they began dating. The publication *The Diplomat* often mixes political reporting with personal drama. Kate is attempting to cope with this, especially considering her complicated relationships with both Hal and Callum.

Leading companies in the UK and US recently experienced what many are calling a very uncomfortable meeting, compared to a famously awkward scene in the TV show *The Bear* where a character dramatically crashed into their own home.

The relationship between these two countries is becoming more unstable, leading Callum to attempt a conversation with Trowbridge. This is a dangerous move that could put both his life and the well-being of his contacts in Russia at risk.

After further discussion, someone proposes a plan for the Americans to enter the submarine and gather photographic evidence confirming Poseidon is inside. They’ll proceed without consulting the British, only revealing their actions afterward – a strategy that’s likely to cause problems, given past experiences.

At the US Embassy, Stuart Heyford is feeling discouraged about his work, but a heartfelt conversation with Eidra Park changes his mind and leads to a romantic connection – it’s all part of the drama unfolding in the third season of *The Diplomat*.

Kate has a new plan involving photos that could save Callum from having to turn himself in – but it depends on Trowbridge cooperating.

Penn shows Trowbridge the submarine photos, explaining that he now has proof to publicly discredit her at the UN. She offers this as a way to show she’s sorry, but Trowbridge refuses, stating that the relationship between their countries is completely fractured.

Penn expressed strong disapproval, stating that countries must either appreciate American aid or face the repercussions of doing without it. He wished them well regardless of their choice.

Trowbridge responds, “Did you really believe confessing to further American deceit would magically make you seem honest? Why should I trust that you wouldn’t just keep it for yourselves?”

Kate steps in then with a new plan, one which might actually pay off.

“You’re right,” she said to Trowbridge. “We can’t be trusted with this. No one should have this much power… It’s too dangerous. Let’s get rid of it, and let it stay lost forever, at the bottom of the sea.”

Trowbridge’s agreement is a major success for the United States, and for the world. Soon after, Hal also experiences a positive turn when Kate becomes upset and repeatedly apologizes to him.

“You have to forgive me,” implores Kate. “You have to take me back. I am so sorry. I’m so sorry.”

“I’m still here,” replies Hal. “We’re still here.”

Despite a difficult and emotional journey, Kate and Hal are truly back together, and it feels right. Recent changes in both their lives have helped Kate understand how important Hal is to her – he simply understands her like no one else does.

What a beautiful way to end the third season, right?

Except, wait. This wouldn’t be The Diplomat if it didn’t end the season with a ginormous bombshell.

After making amends, Callum informs Kate that the Russians have located the submarine, but the Poseidon missile isn’t on board. He’s unsure if his information is correct – he suspects the sensors might be malfunctioning – but he feels something isn’t right about the whole situation, beyond the fact that it involves a hidden underwater operation.

How The Diplomat season 3 twist sets up season 4

As the season wraps up, pictures are taken of everyone involved while Kate prepares to fly back to America with Hal.

She and Grace’s husband watch as Hal and Grace pose together, whispering between each photo.

“Doesn’t it bother you, Kate?” asks Todd. “Their extremely productive working relationship?”

We’ve repeatedly witnessed Todd becoming increasingly worried, but we’ve dismissed his concerns, much like Kate does, and haven’t taken them seriously.

Todd continued, explaining that when he asked her about it, she told him it wasn’t anything romantic – just them secretly planning to take over the world.

It just hit me, and it wasn’t what I expected. I immediately thought Hal was messing around with Grace, but that didn’t make any sense. No, it was something way worse, and the realization totally floored me.

“Did the Russians take [Poseidon] or did you?” she asks Hal.

Hal tries to brush her off, saying, “Let’s talk on the plane.” But Kate’s having none of it.

You manipulated me into misleading the Prime Minister with false information. If the British government discovers this, they’ll see it as a hostile act, potentially an act of war.

Hal warned Kate, “Don’t tell anyone,” before returning to Grace, who then asked if he was alright.

“Not entirely,” says Hal. “She knows.” She being his wife, Kate.

The season concluded with a photographer exclaiming “Wonderful” – an ironic comment, considering the scene involved the world’s two most influential leaders having just secretly taken a highly powerful nuclear weapon from the United Kingdom.

Considering what happened – the President *did* die – this isn’t as shocking as what we saw at the end of last season. Plus, Hal hasn’t exactly built a reputation for being reliable.

What’s really surprising here is Hal’s always been reliable when it comes to Kate. He might stretch the truth or act secretly sometimes, but he’s consistently been her biggest champion when she needed him most.

It would have been impossible to imagine ever deceiving Kate like this – using lies to make her do something so damaging. Especially now, when she was prepared and eager to take on this very role…

Kate and Hal have had a rocky relationship, but this feels like the final blow, especially now that they had finally worked things out and were truly getting back together.

The foundation of *The Diplomat* has always been Kate’s faith in Hal, but that’s now completely broken. This creates a hugely compelling, yet complicated, situation for season four, and could potentially be the show’s finale. It’s hard to see how Kate and Hal, or even the world, can recover from this betrayal.

This cliffhanger isn’t marked by loud arguments like past season finales, but it’s by far the most shocking one yet, fundamentally damaging the connection between Kate and Hal.

The Diplomat season 3 is now available to stream on Netflix.

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2025-10-18 14:21