Billie Eilish just officiated her brother's wedding and broke the internet in an olive green gown

Billie Eilish traded a microphone for a marriage licence at the weekend, officiating her brother Finneas's wedding to Claudia Sulewski in a green gown that instantly became the internet's main character.

The pair married in Montecito on Saturday, capping off an engagement fans had been tracking for months. Sulewski wore an ivory silk ball gown for the ceremony. Eilish wore a fitted, draped green number, called olive by some outlets and sage by others, and somehow made "sister who does the paperwork" the best dressed job at the wedding.

The guest list read like a group chat that could break the internet on its own. Justin and Hailey Bieber were there. So were Emma Chamberlain, Kristen Bell and Dax Shepard, Jason Sudeikis and Rebecca Black. Nobody needed a seating chart, they've all been in each other's Instagram stories for years.

What makes this land isn't the star power, it's the casualness of it. Eilish has a shelf full of Grammys and two Oscars, and she still spent Saturday getting handed a ceremony script like the rest of us handle a group project. Finneas has produced most of her biggest songs. She returned the favour by legally marrying him off.

Fans have already picked apart the dress, the vows and the fact that Eilish, famously allergic to dressing up, chose something this considered for the day. That's the actual headline: an artist known for baggy silhouettes picked a fitted, colour forward gown for one specific reason, because the day was never about her.

Expect the green gown to land on every wedding guest outfit inspo board by the weekend, and Sulewski's ivory gown to spark a hundred bridal Pinterest boards regardless of anyone's actual wedding budget.

Either way, the O'Connell siblings have once again proven they run the family business better than most actual Hollywood dynasties. Watch this space for the group chat screenshots.