Billie Eilish's brother Finneas marries longtime girlfriend Claudia Sulewski… and the pop star officiates the ceremony

Billie Eilish’s brother, Finneas, married his longtime girlfriend, Claudia Sulewski, on Saturday, and the pop star reportedly had the honor of officiating the star-studded ceremony.

The two exchanged vows in a lush garden setting at San Ysidro Ranch in Montecito, California, surrounded by family and friends, as seen in photos obtained by Deuxmoi.

Eilish, 24, who will make her big-screen acting debut in the upcoming movie The Bell Jar, handled her special role at Finneas' wedding while wearing an off-the-shoulder, olive-green gown. Her 31-year-old actor boyfriend, Nat Wolff, was also in attendance.

Other big-name guests included Nina Dobrev, Kristen Bell, Dax Shepard, Justin and Hailey Bieber, Emma Chamberlain, Rachel Sennott, Stassie Karanikolaou, Jason Sudeikis and Carter Gregory.

The beauty influencer bride, 30, had four dresses custom made for the weekend event by Oscar de la Renta, per Vogue, starting with a bias-cut creation with draping back for the rehearsal dinner, then a ballgown with drop-waist bodice and bell-shaped skirt for the ceremony, followed by a reception dress with feathers to get the party started, and ending with a pink and dove-gray after-party frock.

Finneas, 29, who was born Finneas Baird O’Connell, is a singer, songwriter and record producer who is best known for his collaborative work with his ten-time Grammy Award-winning sister.

He wore a classic black tuxedo for his wedding.

Finneas and Sulewski have been together since meeting on the exclusive dating app Raya in 2018.

As he told BuzzFeed, Finneas couldn't get the brunette beauty out of his mind and wrote his song Claudia within hours of meeting her, including the lyrics: 'Oh, I'm in trouble now / Come kiss me black and blue / Might last another round / But I'm gonna fall for you.'

Sulewski was also the inspiration and muse for his 2022 song Mona Lisa, Mona Lisa, and starred in and directed the song's phone-recorded music video.

Last year, Finneas used his seventh anniversary as a 'Trojan horse' to propose to Sulewski.

The musician popped the question last October after seven years of dating, and later revealed he had staged the proposal like a highly calculated, secret operation.

'I think she thought we were going to go do a little staycation at a beach,' Finneas said on Today with Jenna & Sheinelle. 'I was relying on her to be distracted by getting ready in the morning, and maybe sending a work email or something.

'And I drove her to the airport. She was like, "Why are we at the airport?" We got on a helicopter, and I was like, "We're taking a helicopter to a private campsite in the mountains," and I brought a private chef with us. And so he cooked food for us, and then he got back on the helicopter and left.

'We were marooned on the mountainside, and then we just had this really beautiful day out in nature. And then, I did ask [her to marry me].'

Finneas was very nervous ahead of proposing, particularly when it came to hiding the ring so Sulewski couldn't find it until the right moment.

'The ring was in a sock wrapped around another sock in my suitcase. And then there was one point where it was about to happen, and I was, like, 'Hang on. One second.' It was just lies all day,' he quipped.

'And I ran around, and I heard the ring, like, rattling in the box in my pocket. And so I went and hid behind a bush and untied the thing and opened it and tucked it back in its little slot, and then was, like, walking in a sort of ballet pose.'

Earlier this year, Sulewski praised Finneas for wanting to be involved in their wedding planning.

'Finneas has had more input than I think he thought he would have, which is exciting for me because I don't want to feel like I'm planning all this by myself,' she said in a video shared to YouTube.

'I've been really surprised by how many opinions my fiancé has had, and I love it because I want him to feel ownership of this special day for us.'

Sulewski insisted she wouldn't be a 'bridezilla' but she mentioned she did want to be hands-on with the plans.

'As you guys can imagine, yes, I have PDFs, table inspo, florals, seating for the ceremony. I actually think that I will broadly be a Type B bride because I'm a very chill person. Like, I'm not stressed about the scheduling of everything,' she said.

'I'm not stressed about what weekend it lands on. There's a lot of things that I am excited to just kind of go with the flow about and let the wedding plan itself.

'I guess the one Type A thing about myself is that, yes, I will pull inspo, I will spend hours on the computer, I will draw up things and make graphics.' 

She added: 'But that's just me being excited. I guess what I'm trying to say is I don't feel like I'm going to be a bridezilla. Like, this is just going to be fun and filled with love. It's been really exciting to plan so far.'