A guest appearance by someone with a prior professional relationship with one of the cast members of the show, such as Rhea Perlman appearing on Becker, Christopher Lloyd appearing on Spin City, or Helen Hunt appearing on The Simpsons. More often than not, the guest actor will be playing an Old Friend of the relevant character, whom they haven't seen in years.
Subtrope of Casting Gag. Liable to be a Large Ham. Expect numerous Actor Allusions. Compare Real-Life Relative. Not to be confused with Old Friend, Remember the New Guy?, or Beleaguered Childhood Friend, but can overlap with any of them.
Examples:
- In 2022, Progressive paired Flo with Jon Hamm. He and Stephanie Courtney had previously worked together when she played switchboard operator Marge on the first season of Mad Men.
- Episodes 42 and 43 of the Angel Heart anime series involves Ryo Saeba (who is voiced by Akira Kamiya) dating a news reporter voiced by Yuriko Yamamoto. Kamiya and Yamamoto previously played Kenshiro and Yuria in the original 80's version of Hokuto no Ken.
- Beauty and the Beast (1991) featured Jerry Orbach as Lumiere and Angela Lansbury as Mrs. Potts. They were very good friends, having worked together on Broadway and television. Notably, Orbach had a recurring role as hardboiled detective Harry McGraw in Landsbury's Murder, She Wrote.
- Carry On... Series:
- Starting in Carry On Constable, Kenneth Williams and Hattie Jacques were joined by their Hancock's Half Hour co-star, Sid James.
- Joan Sims' Something to Shout About co-star Fenella Fielding had one memorable scene in Carry On Regardless as Mrs. Panting. Four years after Shout About ended, Fielding made one more Carry On appearance as the villainous Valeria Watt in Carry On Screaming!.
- In the same vein, Kenneth Williams' Beyond Our Ken co-star Betty Marsden has one scene in Regardless as Mata Hari. She would return to the series with a bigger role for 1969's Carry On Camping, a year after the two had starred in Round the Horne. Another of Williams and Marsden's co-stars, Bill Pertwee, appeared in the series, playing the barman in Carry On Loving and the Whippet Inn manager in a Deleted Scene from Carry On at Your Convenience.note
- When Madeline Smith was unavailable to play Lily in Carry On Abroad, Sid James recommended Sally Geeson, who was at the time playing his daughter in Bless This House. Geeson returned for Carry On Girls, and as an extra bonus for BTH fans, it was in that film that Robin Askwith, who had appeared in BTH's Non-Serial Movie taking over from series regular Robin Stewart, made his sole Carry On appearance.
- Carry On England: Sergeant Major Bloomer and Gunner Shorthouse were played by Windsor Davies and Melvyn Hayes, who were starring in It Ain't Half Hot, Mum at the same time the film was released. Davies is practically playing the same role in both — that of a perpetually disappointed, constantly shouting Welsh Sergeant Major.
- All Christopher Guest films feature members of his Production Posse in different combinations, but it is particularly noticeable in A Mighty Wind; the Folksmen are played by the three main members of Spinal Tap. The video for a song from their 60s folk-rock phase is clearly a Shout-Out to "Listen To The Flower People".
- The Hobbit:
- Martin Freeman's costar Benedict Cumberbatch from the acclaimed show Sherlock is the voice behind Smaug the dragon. One can already imagine Smaug and Bilbo solving crimes in Middle Earth.
- Martin Freeman and Benedict Cumberbatch aren't the only examples of this. Hugo Weaving and Richard Armitage also both appeared in Captain America: The First Avenger.
- And Graham McTavish guest-starred in an episode of Pushing Daisies, where Lee Pace played the main character.
- And Orlando Bloom (as the Duke of Buckingham) and Luke Evans (as Aramis) were in The Three Musketeers (2011) together.
- Interception, the Short Film reunites Alimi Ballard with NUMB3RS co-stars Rob Morrow and Dylan Bruno.
- Into My Heart (1998):
- Claire Forlani and Jake Weber previously worked together on Meet Joe Black.
- Rob Morrow and Jayne Brook previously worked together on Last Dance.
- Seeing James Spader as the main villain opposing a group led by Robert Downey Jr. in Avengers: Age of Ultron is amusing, considering the two had previously worked together a few times in the 1980s. They actually played best friends in Tuff Turf, as well as slightly antagonistic associates in Less Than Zero.
- In Maverick (directed by Richard Donner), Bret Maverick (played by Mel Gibson) is in a bank that is held up by a gang, one of whom is played by Danny Glover (Gibson's co-star from the Lethal Weapon movies, also directed by Donner); the two men almost appear to recognize each other, but then dismiss the notion. (Then, to cement the association, as Glover's character is mounting his horse for a getaway he is heard to say, "I'm gettin' too old for this shit!" - Roger Murtaugh's famous catchphrase from Lethal Weapon.)
- Extreme example: In the Mystery Science Theater 3000-featured film Quest of the Delta Knights all sorts of hilariously awkward dialogue of this sort occurs between the Big Bad (David Warner) and The Mentor (David Warner).
Crow: "David Warner, you're under arrest by the order of David Warner!"
- On the Buses: Vera, one of the new female drivers, is played by Pat Coombs, who had previously starred with Reg Varney as married couple Harry and Lana Butt in Beggar My Neighbour.
- Prom Wars: Joe and Sabina's performers played a couple in Hatley High, which they filmed not too long before this movie, and dance together in one scene after Sabina sees that Joe has a crush on Jen B. and makes him look more widely-desired to help get her attention.
- In Quid Pro Quo, Dylan Bruno previously worked with James Frain, Joshua Leonard, and Kate Burton previously worked together on NUMB3RS.
- Robin Askwith is reunited with his On the House co-star John Junkin in the final two films of the Confessions of a... Series — Junkin only has a single scene in Confessions of a Driving Instructor as Italian restaurant owner Luigi, while in Confessions from a Holiday Camp, he plays Timmy's tyrannical boss, Mr. Whitemonk.
- In The Senator Was Indiscreet, a William Powell vehicle, the final scene reveals that his wife, unseen till now, is Myrna Loy, who co-starred as his wife in numerous movies including The Thin Man series.
- One of the best moments of Shark Tale was when Robert De Niro said to Martin Scorsese, "We've worked together for a real long time."
- John Cho and Anton Yelchin, who played Sulu and Chekov in the Star Trek "Kelvin Timeline" films that started with the 2009 reboot, previously crossed paths before in the 2001 film Delivering Milo.
- Tomorrow Never Dies opens with Bond on a mission with M and Admiral Roebuck of the Royal Navy supervising. M (Judi Dench) and Roebuck (Geoffrey Palmer) previously starred together in the series As Time Goes By.
- Triple Frontier co-stars Oscar Isaac and Pedro Pascal previously both performed in the Off-Broadway play The Beauty of the Father, where the actors formed a long-lasting friendship.
- We Can Be Heroes (2020) features Pedro Pascal and Boyd Holbrook as members of the same superhero team, four years after they co-starred on Narcos as DEA partners.
- Chance to Fly is written by Ali Stroker and Stacy Davidowitz. Ali Stroker is best known for her acting, being the first performer in a wheelchair to get the lead role in any Broadway production in history. She also guest starred in Glee. The review on the cover of her novel was written by Chris Colfer, another Glee-actor-turned-author-of-middle-grade-fiction.
- After being defeated by Son of Havok at Lucha Underground, Sexy Star took him on with Chavo Guerrero Jr.. Havok, who some wrestling might have known better as Matt Cross, in turn teamed up with fellow Tough Enough contestant Ivelisse Vélez.
- Camelot was written and originally produced by much of the same team responsible for My Fair Lady (including director Moss Hart in the last Broadway show of his life). Not only did Julie Andrews have the starring role in both productions, but Robert Coote, who was Pickering in My Fair Lady, returned as Sir Pellinore in Camelot.
- Catherine Tate and David Tennant of Doctor Who fame were reunited for an onstage production of William Shakespeare's Much Ado About Nothing. They are both prominently featured in its advertising. (The two are also close friends in real life.)
- In the Mass Effect series Female Shepard and Ashley Williams are voiced by Jennifer Hale and Kimberly Brooks. The two have worked together as partners before... specifically band-mates Thorn and Luna from the various Scooby-Doo movies and shows. This makes it funnier if you have a female Shepard and always include Ashley in your squad and then turn the Hex Girls song on while playing.
- In the Adventure Time episode "Everything's Jake", the character Jake is trapped in his own body and meets a guy called Goose. Although Jake has never seen Goose before, Goose claims that Jake is an old friend. This is because Goose's voice actor, Billy West, and Jake's voice actor, John DiMaggio, voiced the main characters Fry and Bender in Futurama.
- In Avatar: The Last Airbender, Grey DeLisle voices Azula, and Mark Hamill voices her father, Fire Lord Ozai. In a third season episode of Danny Phantom, the ghost of the week, Undergrowth, is voiced by Mark Hamill, and Sam Manson is voiced by Grey DeLisle. When Undergrowth takes control of Sam's mind, she even calls him "father".
- The Avengers: Earth's Mightiest Heroes: David Kaufman, known among other things for being the voice of Danny Phantom, showed up in "The Private War of Doctor Doom", reprising his role of the Human Torch from past Marvel video games. Regular series heroine the Wasp is voiced by Colleen O'Shaughnessey, who voiced Danny's sister Jazz Fenton. Reportedly, the two were excited to be working together again.
- The Batman (2004): "A Matter of Family", the episode that introduced Robin, featured Kevin Conroy (Batman from the DCAU) as Dick Grayson's father and Mark Hamill (Joker in also the DCAU) as Tony Zucco. That same episode also included Grey DeLisle as Dick Grayson's mother. Hamill and DeLisle voiced father and daughter Ozai and Azula on Avatar: The Last Airbender.
- Batman: The Brave and the Bold:
- Blue Beetle (Will Friedle)'s best friend Paco is played by Jason Marsden, who previously played Eric Matthews (also Friedle)' best friend, er, Jason Marsden on Boy Meets World. The two actors are best friends in Real Life, so this sort of thing happens a lot with them.
- Kevin Conroy, the voice of Batman in the DC Animated Universe, played the Phantom Stranger in "Chill of the Night!" alongside Mark Hamill, who famously played the Joker in the DCAU as well, as the Spectre. The episode also featured Adam West and Julie Newmar (Batman and Catwoman from the 1966 series) as Thomas and Martha Wayne.
- "The Super-Batman of Planet X!" also featured Kevin Conroy as the Batman of Planet Zur-En-Ar. Since he's a Composite Character of Batman and Superman, his extended cast includes expies of Lois Lane and Lex Luthor voiced by Dana Delany and Clancy Brown, who played those roles in both Superman: The Animated Series and Justice League alongside Conroy as the Dark Knight.
- In the sequels to Disney's Cinderella, Prince Charming is voiced by Christopher Daniel Barnes and Cinderella herself is voiced by Jennifer Hale. The two of them were previously the voices of Spider-Man and Black Cat respectively in Spider-Man: The Animated Series. Also, during the run of said series, Robert Hays reprised his role of Iron Man for some team-ups with Spider-Man. Hays and Barnes previously appeared together on the Starman TV series and both were reportedly thrilled with working together again.
- One episode of Clifford the Big Red Dog had T-Bone (voiced by Kel Mitchell) meeting an old friend, Hamburger (Played by Kenan Thompson). If you're old enough, you'd remember that both of them starred together in two shows prior to breaking up due to creative differences.
- Tara Strong and Cree Summer have been friends since childhood, even growing up together, and these days do a lot of voice-over work together. In other words, if you hear one of them in a given series, you're likely to hear the other in the same series at some point. They've done enough shows together that their respective characters eventually parodied the infamous Sweeps Week Lesbian Kiss.
- A lot of cartoon voice actors do this with people like Tara and Cree, as well as Grey DeLisle, Tom Kenny, Kevin Michael Richardson, Rob Paulsen, Carlos Alazraqui, the list could go on.
- In DuckTales (2017), arch-enemies Scrooge McDuck and Magica DeSpell are played by David Tennant and Catherine Tate respectively. Tennant and Tate were the Tenth Doctor and his best friend Donna Noble respectively on Doctor Who.
- In Harriet the Spy, the child psychologist Harriet visits is voiced by Michelle Trachtenberg, who played Harriet in the 1996 movie.
- When Pleakley's family comes to visit on Lilo & Stitch: The Series, they are voiced by many of Kevin MacDonald's former castmates from The Kids in the Hall. The only Kid in the Hall who didn't voice a family member voiced a preacher in that episode.
- In The Magic School Bus, several guest stars were friends of Lily Tomlin (Miss Frizzle), most notably Dolly Parton, her 9 to 5 co-star, who appeared as Miss Frizzle's cousin Katrina Eloise "Murph" Murphy in the "Holiday Special" episode.
- In The Mighty B!, Andy Richter voices Amy Poehler's little brother. On Late Night with Conan O'Brien, Poehler played Richter's little sister in a few sketches in the late 90s.
- After they both starred on The Suite Life of Zack & Cody, Brenda Song played a rival to Ashley Tisdale's Candace on Phineas and Ferb.
- Thomas Sangster played a young boy with a Precocious Crush on Olivia Olsen's character in Love Actually—so when they were cast as Ferb and Vanessa respectively, Ferb's crush on Vanessa became a Running Gag.
- In The Simpsons, Sideshow Bob is played by Kelsey Grammer. His brother and father are played by David Hyde Pierce and John Mahoney respectively, who played Frasier's brother and father.
- In Steven Universe, Greg Universe and his former manager, Marty, are voiced by Tom Scharpling and Jon Wurster of the radio show/podcast The Best Show. Compounding the Casting Gag is that despite the real-life duo being great friends and well-known comedy performers, Marty was such an utterly despicable black hole of a person (similar to awful characters Wurster tends to portray on The Best Show, like the Gorch or Timmy von Trimble) and abused Greg so badly that Greg now considers him "dead to me", even though he was indirectly responsible for Greg meeting Rose.
- Scharpling and Wurster reprise this schtick in an episode of Adventure Time, with Scharpling as Jake's brother Jermaine and Wurster as an evil demon Jermaine has trapped.
- In an episode of Kiff Scharpling plays Rob Sadly, an old classmate of series regular Ms. Deer Teacher, voiced by Deedee Magno Hall, who voiced Pearl.
- The casting of Michael Donovan as Sabretooth opposite Scott McNeil as Wolverine in X-Men: Evolution is rather amusing considering their respective roles as Billy and Jimmy Lee.

