Everything To Know About ‘The Diplomat’ Season 4 After Season 3’s Twist Ending

Warning: Spoilers ahead for The Diplomat Season 3.

After another politically chaotic season of The Diplomat, fans are already wondering what’s next for Kate Wyler (Keri Russel) and Hal Wyler (Rufus Sewell). But it’s the final quiet moments of the finale that raise the loudest questions: What could happen in Season 4 after that jaw-dropping twist with the Poseidon missile?

The Diplomat’s eight-episode third season begins with Vice President Grace Penn assuming the presidency after the shocking death of President William Rayburn. However, one of Penn’s surprising first decisions in office is to appoint Hal as her vice president, even though Kate wanted the job, which worsens her tumultuous relationship with her husband.

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With Hal now Vice President, Kate resumes her role as ambassador to the U.K. They decide to stay together publicly but move toward a private divorce, allowing them to see other people. “Publicly, they’re still married. Privately, they know that they’re not, although Hal is never a give-up kind of guy,” Cahn continued. Season 3 toggles back and forth between the beginning of Hal and Kate’s relationship and the present day.

In the finale, Kate recommits to Hal and asks him to take her back. But the twist ending in the final seconds of Season 3 could change everything — and force her to question whether she knows him at all.

How Does The Diplomat Season 3 End?

In the final seconds of Episode 8, Kate Wyler makes a startling discovery. She believes that Hal and Grace conspired together to steal the Poseidon missile, a Russian nuclear weapon of doomsday-level destruction, for the U.S.

The Poseidon was being kept on a disabled Russian submarine off the coast of England. Nicol agrees to have it covered in concrete and hidden on the ocean floor. However, British spy, Callum Ellis (Aidan Turner), Kate’s secret love interest in Season 3, tells her that the Russians found the sub and took the Poseidon.

But it wasn’t the Russians, after all. Kate pieces together that it was the Americans (Grace told Trowbridge that the U.S. sent an unmanned drone to take photos of the sub). That’s when they sent a submarine big enough to hold the Poseidon to steal it.

“It’s pretty bad,” series creator and executive producer Debora Cahn told USA Today about Kate’s predicament in the finale. Kate “is going through this experience in which her vision of who (Hal is) keeps changing and shifting. And just as soon as she feels like she understands who he is and understands who she is herself, the picture shifts radically.”

When Kate confronts Hal — concerned that the theft could lead to a war between Russia and the U.K. if the Russians think the British were behind it — Hal forbids her from saying anything. “You will tell no one,” he says. He then walks over to President Penn and whispers, “She knows.”

Allison Janney, who portrays Penn, told The Hollywood Reporter that she physically threw her script across the room when she read the chilling ending.

“To have made this unbelievable, dark and secret decision — and seeing that Kate knows, just by looking at her, I know she’s going to be trouble for us,” Janney explained. She added that the fourth season will start with that secret — but it won’t be the only one lurking behind closed doors.

She continued, “I know season [four] is going to start with that secret. There’s lots of secrets in this show, lots of decisions being made behind a closed door, and then behind another closed door… it makes for very, very compelling drama.”

Where Will Kate And Hal’s Relationship Go In Season 4?

It’s unclear where Kate and Hal’s relationship is headed in Season 4, but things are bound to get messy. Before Kate discovered her husband’s betrayal involving the Poseidon missile, she apologized and asked him to take her back. Hal accepted her apology and assured her that he was “still here.”

Cahn confirmed to THR that setting the stage for this intimate moment between the couple was intentional, saying she wanted it to feel as though they were on “solid ground” again before throwing in another curveball.

“We wanted to bring the characters to a place where, just when they felt like they were on solid ground again, the lens shifts and Kate is seeing something new in Hal that she hadn’t anticipated and believing that she, after decades with this person, understood what she was getting, and then finding out that the game keeps shifting, no matter how much time you commit yourself to having it stand still.”

However, Hal betraying both and their country goes against everything Kate stands for.

“That’s the thing about Kate. She’s a true public servant; she is a civil servant of the government,” Russell added. “She loves the country, she believes in it. She really is one of those true people. I don’t think she is corrupted by power. That’s what’s great about her. This is a crazy line to cross that I do not think Kate would ever make, and Hal is easier with those blurry choices.”

Russell told Tudum that in the aftermath of Season 3, the “unraveling will be fun.” Sewell agreed, adding, “Whether Kate and Hal are warring, whether they’re together, whether there’s other people, it’s fun for us, whatever’s happening,” he said.

Will There Be The Diplomat Season 4?

Yes, Netflix renewed The Diplomat for a fourth season in May 2025. The exciting announcement was made by Netflix chief content officer Bela Bajaria on stage at the Netflix Upfront in New York City, Variety reported at the time.

Although the third season dropped on Oct. 16, the show is wasting no time before starting Season 4. Netflix confirmed that production for the next installment begins this fall.

What Will The Diplomat Season 4 Be About?

The Diplomat Season 4 will pick up after the Season 3 finale, following President Penn and Vice President Hal’s shocking plan to steal the Poseidon missile for the U.S. — a move that could have grave consequences for the U.K., U.S., Russia, and the entire world.

When asked by Collider about what could unfold in Season 4, Cahn said that although the writing sometimes changes as the story unfolds, the team plans to explore the power dynamics between Kate, Grace, and Hal.

“What does it mean to have two powerful women with one powerful man stuck in the middle of them?” the showrunner said. “How do those relationships impact each other and change each other?”

She continued, “Hal is in a different relationship right now. He has a very, very potent and important relationship developing and succeeding with another woman who happens to be the President of the United States. The idea that that was not going to change the chemistry of the marriage was also magical thinking.”

Cahn also teased to Tudum that fans “should be worried” heading into Season 4. “There’s plenty to worry about,” she said. “It can be pretty chilling when you see who takes power and get the sense that they may be horrifically misusing it.”

Who Will Be In The Diplomat Season 4 Cast?

While the streamer hasn’t confirmed the full cast for The Diplomat Season 4, several returning actors have been announced.

Lead stars Russell and Sewell will reprise their roles in the next installment. West Wing co-stars Janney and Bradley Whitford are also returning for the upcoming season and have been promoted to series regulars, according to Tudum.

“It was such a treat to have the four of them together, to be able to look at Keri and Rufus and Allison and Brad working together. It’s like the greatest game of doubles tennis you’ve ever seen,” Cahn told THR.

When Is The Diplomat Season 4 Release Date?

Netflix hasn’t announced a release date for The Diplomat Season 4 yet. Based on the release pattern of the previous three seasons, the fourth season will likely premiere in fall 2026. Season 1 arrived on Netflix in April 2023, Season 2 in October 2024, and Season 3 in October 2025.

With production for the fourth installment already underway, a 2026 premiere date seems likely, or, at the latest, 2027. The streamer is expected to release more details in early 2026.

The Diplomat Season 3 is streaming on Netflix. Watch the official trailer below.