Lukadrinette

Lukadrinette is the polyship ship between Adrien Agreste, Marinette Dupain-Cheng and Luka Couffaine from the Miraculous Ladybug fandom.

Canon
Marinette and Adrien both met Luka on his boat house during the music festival, and while Adrien is Marinette's long held crush, just as Ladybug is Adrien's, Marinette had began to develop feelings for Luka shortly after she met him; who also has a crush on Marinette. Because of this Marinette begins to question her old and new feelings for the two boys, which is why she froze in front of them when they both offered to help Marinette get up from the spot she ended up in when she sild and fell on the ice, as she felt on her end that she has been placed in a position where she might have to decide between the two. When Luka notices that Marinette has feelings for Adrien, he tells her that she should go and talk to him, Marinette thanks Luka for his advice with a kiss before she dashes over to Adrien.

Season 2
Captain Hardrock
 * The end card is of Marinette blushing, while she is "standing" between Adrien and Luka, who might be looking at each other with a smile.

Frightningale
 * The trio are seen dancing together in a scene from Clara Nightingale's music video, with the two boys wearing a Ladybug mask while Marinette's is of a black Chat Noir mask.

Frozer
 * As Adrien sees Marinette and Luka getting ready to skate together, he goes up to her.
 * When Marinette fell down at the ice rink, both Adrien and Luka officered to help her back up while smiling at her.
 * The three are seen in the end, where Marinette is seen as her civilian and superheroine self.

Fanon
The ship could simply be due to Marinette having romantic feelings for both boys, who are friends of hers and have their own romantic feelings for her. Some have Lukadrinette rival with Adrigaminette (Adrien, Kagami x Marinette), since they both serve as compromise ships.

Some have Adrien view Luka as a love rival for Marinette's affections, once he begins to develop feelings for her alone, consciously or unconsciously. As there have been sighs of Adrien possibly being jealous of Luka or slowly realizing his feelings for Marinette, from when he first saw them together at the rink.

Because the leaks about Marinette, Adrien and Luka's upcoming superhero forms were reveled at the same time, it inspired fans to do fan artwork of Cat Noir, Multimouse (Marinette through the Mouse/Rat Miraculous) and Viperion together; despite knowing that cats and snakes eat mice.

Since the season two episode, "Timetagger", reveals that during the time of their adulthood, Ladybug and Cat Noir have assembled a team of fellow Miraculous holders, that might have Luka as one of its members.

On AO3, poly the ship has over 46 fanfics.

Fandom
FAN FICTION
 * Marinette/Adrien/Luka on FanFiction.Net
 * Marinette/Adrien/Luka on FanFiction.Net

TUMBLR

Trivia

 * According to Feri González, Luka isn't limited to the role of alternate love interest, the same with Kagami Tsurugi.
 * All three of them are Jagged Stone fans.
 * Adrien had once played the part of keyboard player as a guest member in Luka's band, Kitty Section, while Marinette had designed costumes for the rock band.
 * Even though Adrien wasn't playing with them during that time.
 * Luka's younger sister, Juleka is one of Marinette and Adrien's classmates.
 * The out of order released episode "Party Crasher" reviles that sometime before the events of it, Luka will become one of Ladybug and Cat Noir's occasionally allies whenever he is given the Snake Miraculous so he could help them as the snake-themed superhero, Viperion.
 * Even though fans knew for sometime that Luka would one day receive the Snake Miraculous, from concept art leaks that revel Luka's superhero title, form and weapon; as well as the forms and titles that Marinette and Adrien would go by from using the other Miraculouses on themselves in the future.

Variations

 * Adrienette refers to the ship between Adrien and Marinette
 * Lukadrien refers to the ship between Luka and Adrien
 * Lukanette refers to the ship between Luka and Marinette