Question: Which actress appeared as Ariadni in Before Midnight?
About the article "Before Midnight (film)", section "Cast".

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Pavlos and Christina's relationship becomes much more serious after he is diagnosed with a potentially fatal blood condition, the first time they don't make it to the altar and both decide to not turn up to their wedding.
The second time, Christina goes to the wrong church on the day of the wedding, however they finally marry and soon after they marry, a male donor is found for Pavlos' condition and all is well.
However, Christina quickly finds herself infatuated with the donor Manos and Pavlos with the donor's girlfriend Ariadni.
Myrtle is aware of the affairs that have risen from these infatuations, and is deeply worried about both of the newly-weds.
Christina has recently become best friends with the donor's now ex-girlfriend, Ariadni, after the couples engaged in a sort of story similar to a real life wife swap.
The 4 people have now split up, with Manos going to Iraq to work on photography, as an attempt to get over his relationships with Ariadni and Christina and Christina and Ariadni avoiding Pavlos to try to get over their relationships with him.
Pavlos is constantly seeking relationship advice from Hector and his brother, which provides some of the comic relief in this storyline. 
Feature films.
Director "The Slow Business of Going" (2000) "2" (2007), screen adaptation director, conceived and directed for the stage by Dimitris Papaioannou "Attenberg" (2010) "Prometheus in Athens" (2011), screen adaptation director, conceived and directed for the stage by Rimini Protokoll Screenwriter "The Slow Business of Going" (2000) "Attenberg" (2010) Producer "Kinetta" (2005), directed by Yorgos Lanthimos "Palestine Blues" (2006), directed by Nida Sinnokrot "Dogtooth" (2007), directed by Yorgos Lanthimos, associate producer "Lovers of Hate" (2010), directed by Bryan Poyser, executive producer "Alps" (2011), directed by Yorgos Lanthimos "Pearblossom Hwy" (2012), directed by Mike Ott "Before Midnight" (2013), directed by Richard Linklater Actor  "Slacker" as Cousin from Greece  "Before Midnight" as Ariadni  
 Ethan Hawke as Jesse
 Julie Delpy as Céline
 Seamus Davey-Fitzpatrick as Hank
 Jennifer Prior as Ella
 Charlotte Prior as Nina
 Xenia Kalogeropoulou as Natalia
 Walter Lassally as Patrick
 Ariane Labed as Anna
 Yiannis Papadopoulos as Achilleas
 Athina Rachel Tsangari as Ariadni
 Panos Koronis as Stefanos
At the beginning of the third season, Christina and Pavlos are getting a divorce and fight constantly whenever they are near each other, or avoid each other completely.
However, they later realise their love for each other, and decide that they will still get a divorce, but remain together as a couple.
However, during this reunion, Pavlos resumed his relationship with Ariadni who claims that she doesn't mind that Pavlos is back together with Christina, but is secretly plotting her revenge.
Pavlos is then meeting with Ariadni when they hear shotguns and Pavlos goes to see if the person is wounded when he also gets shot.
He tells Ariadni to stay and he goes to Ektora who takes him to the hospital under a false name.
He and his family try to keep his meeting with Ariadni a secret.
He then realises that he shouldn't treat Christina this was and breaks up with Ariadni.
Content on ruining Pavlos' life she then joins with Avgeri and labels people in his family as the murderers After time Christina gets a call that the divorce has gone through.
Realizing that she forgot to tell her lawyer to cancel the divorce.
When Pavlos finds out he gets mad but then sees the romance in Marrying Christina again.
When Ariadni finds out she does everything she can to try and stop the wedding even go there on the day and say she was having an affair with Pavlos a second time.
Renos and Dimitri makes sure she doesn't.
But after the honeymoon she tells Christina finds out.
She doesn't let this ruin her marriage with Pavlos and turns it around onto Ariadni saying she manipulated both she and Pavlos. 
Ethan Green Hawke (born November 6, 1970) is an American actor, writer and director.
He has been nominated for the Academy Awards both as an actor and a writer.
He also received a Tony Award nomination for his theater work.
Hawke made his film debut in 1985 with the science-fiction feature "Explorers", before making a breakthrough appearance in the 1989 drama "Dead Poets Society".
He then appeared in such films as "White Fang" (1991), "A Midnight Clear" (1992), and "Alive" (1993) before taking a role in the 1994 Generation X drama "Reality Bites", for which he received critical praise.
In 1995 he starred in the romantic drama "Before Sunrise", and later in its sequels "Before Sunset" (2004) and "Before Midnight" (2013).
In 2001, Hawke played a young police officer in "Training Day", for which he received the Screen Actors Guild and Academy Award nominations in the Best Supporting Actor category.
He also garnered two screenwriting Oscar nominations for co-writing the screenplays of "Before Sunset" and "Before Midnight".
Other films have included the science-fiction drama "Gattaca" (1997), the contemporary adaptation of "Hamlet" (2000), the action thriller "Assault on Precinct 13" (2005), the crime drama "Before the Devil Knows You're Dead" (2007), and the horror film "Sinister" (2012).
Hawke has appeared in many theater productions including "The Seagull", "Henry IV", "Hurlyburly", "The Cherry Orchard", "The Winter's Tale" and "The Coast of Utopia", for which he earned a Tony Award nomination for Best Featured Actor.
Aside from acting, Hawke has directed two feature films and three Off-Broadway plays.
He also wrote the novels "The Hottest State" (1996) and "Ash Wednesday" (2002).
Between 1998 to 2005 Hawke was married to actress Uma Thurman, with whom he has two children.
Since 2008 he has been married to Ryan Hawke (née Shawhughes), and they have two daughters.