Sir Paul McCartney to be Stephen Colbert's final guest on The Late Show

Sir Paul McCartney will be the final guest on Stephen Colbert's "The Late Show," airing on his last episode. The legendary musician will sit down with the host for a chat about the Beatles, his latest album, and his frustration with iPhone updates.

Amid speculation as to who would grace the couch at the Ed Sullivan Theater for the final time — and an extended riff on whether Colbert would land Pope Leo XIV, often mentioned as his ideal interviewee — Sir Paul strode onto the stage to applause from the audience, in the theatre where the Beatles made their first US TV appearance in 1964.

The reveal came after Colbert first addressed the audience in a more intimate style than his typical monologue, leaning on his desk as he spoke about the joy hosting The Late Show has brought to him and his staff over the past 11 years.

"This show, I want you to know, has been a joy for us to do for you," he said.

He also referenced his previous comedy persona — the fictional conservative cable host of the same name, from his days on Comedy Central — and spoke about how his time helming CBS's flagship late-night franchise had been different.

"On night one of The Colbert Report back in the day, I said anyone can read the news to you. I promised to feel the news at you," he said.

"And I realised pretty soon in this job, that our job over here was different.

The Late Show's cancellation was officially announced last July, setting off a storm of controversy as it came while CBS's parent company, Paramount, was seeking FCC approval for a merger with Skydance, creating one of America's largest entertainment companies.

Colbert, one of US President Donald Trump's most vocal critics, had just days earlier castigated CBS for settling a lawsuit filed by the president against 60 Minutes for $US16 million ($22 million), despite many legal experts believing the case had little chance of success (Colbert called the settlement a "big fat bribe").

Colbert has mercilessly joked about the network's decision in the months following the announcement, including by inviting former Late Show host David Letterman onto the roof of the Ed Sullivan Theater to engage in "wanton destruction of CBS property".

But while the network came in for plenty more jibes during the course of the finale, the episode was largely an apolitical affair, with the president copping only a few stray asides.

Colbert appeared to want his final episode to steer clear of any bitterness, or even the heartfelt sign-offs that marked Letterman's farewell in the same theatre and Conan O'Brien's final Tonight Show.

In keeping with his opening statement about joy, the Emmy-winning host instead rolled out a series of light-hearted celebrity cameos over the course of the night, laughing through exchanges with high-profile stars such as Ryan Reynolds and Bryan Cranston, and pleading with a recalcitrant (fake) pope who refused to come out of his dressing room.

An extended sequence in which Colbert and his set were sucked into a giant green wormhole featured appearances by Neil DeGrasse Tyson, Colbert's longtime comedy foil Jon Stewart, and fellow late-night hosts Jimmy Kimmel, Jimmy Fallon, John Oliver and Seth Meyers.

"We had one of those, but it only lasted for three days," Kimmel quipped, upon seeing the wormhole.

It also wouldn't have been late-night TV if it hadn't finished with a song.

Colbert — an occasional contributor to his guests' performances (not to the extent of Fallon, but to a much greater extent than Letterman, who would have been hiding in the dressing room with the pope) — gifted us two, the first being a pre-recorded cover of Elvis Costello's Jump Up, featuring Costello and Colbert's former bandleader, Jon Batiste.

Sir Paul then took to the stage with his famous Höfner 500/1 violin bass to lead the studio audience in a joyful rendition of The Beatles' Hello, Goodbye, with what appeared to be friends and family of the show's crew filling the stage.

CBS's 33-year late-night franchise finished with a shot of the Ed Sullivan Theater shrunk down into a snow globe, before the network threw straight to Byron Allen's Comics Unleashed — the low-cost, low-risk replacement (Allen has pledged to avoid politics on the show) that will take over the 11:35pm time slot from next week.

As the late, great Norm McDonald once said of his own appearance on Allen's program, he "couldn't have been more leashed".