Colin Firth as Jamie
Colin Firth actually only jumped into water that was 18 inches deep for the scene when Aurelia dives into the lake after Jamie's manuscript. He and Lúcia Moniz apparently had to crouch down low in order to pretend that the water was deeper.
Alan Rickman as Harry
Alan Rickman actually previously co-starred in a movie with Emma Thompson and Hugh Grant in 1995's Sense and Sensibility. In fact, the only major co-star from Sense and Sensibility who was not also in Love Actually was Kate Winslet -- who still makes a (sort of) cameo in a scene where Daniel and Sam are watching Titanic.
Emma Thompson as Karen
Emma Thompson actually wore a fat suit in Love Actually so as to appear heavier than she actually was in real life.
Hugh Grant as David
Hugh Grant actually did not at all want to do the dancing scene -- according to director Richard Curtis, Grant was "really grumpy" about it, as he did not want his Prime Minister to appear fake.
Keira Knightley as Juliet
Kiera Knightly actually was only 18 when Love Actually was released. She went on to star in the first three Pirates Of The Caribbean movies and become a huge movie star in her own right.
Lúcia Moniz as Aurélia
Lucia Moniz actually came in 6th place representing Portugal in the 1996 Eurovision song contest. The filmmakers also spent 45 minutes debating over what color her underwear should be for the scene where she dives into the lake after Jamie's manuscript.
Liam Neeson as Daniel
Liam Neeson actually has a habit of chewing on toothpicks -- a habit he picked up after quitting smoking.
Thomas Brodie-Sangster as Sam
Thomas Brodie-Sangster actually didn’t know how to play the drums before the film — he was taught by his dad. Also, Brodie-Sangster not only played a 13-year-old boy in the film, but would go on to play a 13-year-old boy again in Games of Thrones… ten years later.
Bill Nighy as Billy Mack
Bill Nighy actually fought super hard for Billy Mack's flashy Love Actually look -- originally, director Richard Curtis wanted to tone down Billy Mack's costumes, but gave in at Nighy's insistence.
Gregor Fisher as Joe
Gregor Fisher actually has a small, uncredited cameo in Shuan of the Dead which also stars his Love Actually co-star Bill Nighy.
Martine McCutcheon as Natalie
Martine McCutcheon actually has expressed pretty solid interest in doing a Love Actually 2, though she admits that it's tough to improve on perfection.
Chiwetel Ejiofor as Peter
Chiwetel Ejiofor actually would go on to star in 12 Years A Slave.
Andrew Lincoln as Mark
Andrew Lincoln actually physically wrote out the famous Love Actually cards upon which he declares his love to Keira Knightley's character (in case you were curious about his handwriting). He would also go on to star as Rick Grimes in The Walking Dead.
Laura Linney as Sarah
Laura Linney actually wishes her character, Sarah, had not picked up the phone call from her brother, which kept her away from Karl. Linney most recently starred in 2013’s The Fifth Estate, and her Showtime series The Big C finished its 4 season run in 2013.
Rodrigo Santoro as Karl
Rodrigo Santoro actually went on to play Xerxes in the 300 movies, and is also a general all-around foxy human.
Kris Marshall as Colin
Kris Marshall actually loved filming so much that he returned his paycheck for the day when he filmed the scene where he charms January Jones and Eliza Dushku in the American bar.
Martin Freeman as John
Martin Freeman actually has his entire plot line cut (where he and another body double, Judy, fall in love while acting out sex scenes) out of Love Actually when the movie airs on ABC Family. Which is probably fine, he's got that Sherlock and The Hobbit money to keep him happy.
Joanna Page as Judy
Joanna Page actually is a serious dramatic actress who spent 10 years acting in dramas for the National Theatre and Royal Shakespeare Company, despite being best known for her more comic roles (namely Stacey on the BBC’s hit show Gavin & Stacey).
Heike Makatsch as Mia
Heike Makatsch actually was dating Daniel Craig while she was filming Love Actually (she was with him for seven years).
Olivia Olson as Joanna
Olivia Olsen actually sang "All I Want For Christmas Is You" for Love Actually -- but her voice ended up being so powerful that Director Richard Curtis had to tone it down in post-production so that she sounded more like a child.
Rowan Atkinson as Rufus
Rowan Atkins actually provided the voice of Zazu in The Lion King, but of course he is best known for his iconic, but quiet character, Mr. Bean.
Claudia Schiffer as Carol
Claudia Schiffer actually wasn’t even supposed to be in the movie — they tried to find someone who looked similar to Claudia Schiffer and eventually decided to go and get the real thing.
January Jones as Jeannie
January Jones actually was a relatively little-known actress when she played Jeannie, one of the blond Americans Colin Frissell successfully seduces with his British accent. She, of course, went on to star as Betty Draper in Mad Men.
Elisha Cuthbert as Carol-Anne
Elisha Cuthbert actually was allowed improvise a lot of her scene with January Jones and Kris Marshall in the American bar.
Billy-Bob Thornton as The U.S. President
Billy-Bob Thornton actually is afraid of antique furniture (yes, really), and during the shoot, Hugh Grant would try and freak him out by briefly “flashing him” with pieces of antique furnishings.