Justin Bieber's Coachella performance alongside Billie Eilish leaves fans shocked as they realise who her famous mum is

On Saturday night, while Billie Eilish was being serenaded by Coachella headliner Justin Bieber, fans made an unexpected discovery about the 'Bad Guy' hit-maker's upbringing.

A beaming Billie, 24, was dragged up on stage on 18 April for Justin's long-awaited performance of 'One Less Lonely Girl', one of the best-loved tracks from his 2009 debut album My World.

Justin's wife, make-up guru Hailey Bieber, had been dancing along with Billie moments prior, as the pair stood in the front of the festival's VIP box. Hailey then pushed her pal up onto the stage when the gushy track's opening lines were heard.

'What Was I Made For' singer Billie could be seen laughing in astonishment and covering her face with both hands as she strode over to Justin, 32, as he sang the chorus at her.

She then fell to her knees as the late-00s anthem drew to a close.

The interaction has since gone viral online, with fans overjoyed to see long-time pals Justin and Billie crossing paths in public once again.

Oddly, however, the sweet moment has since sparked online discussions surrounding Billie's rise to fame, including whether or not she had any famous parents helping her out along the way.

And as it turns out, she does.

Who is Billie Eilish's mum?

Billie's mother is actress Maggie Baird, who also watched Bieber perform live over the weekend for the A-list festival's second weekend.

Maggie starred in several hit TV series in the 00s, including Bones, The X-Files and Six Feet Under.

She also appeared during an episode of Friends in 1999 as a casting director for a dog food commercial audition that Joey Tribbiani (Matt LeBlanc) attends, despite having been diagnosed with a hernia and losing his medical insurance. Remember?

In more recent years, however, the 67-year-old has turned her attention to voice acting. During her daughter's latest on-stage stint, fans learned that she'd actually voiced one of their favourite video game characters, Samara, from the Mass Effect game series, as well as several from Saints Row.

"An actual fun fact about Billie Eilish's mum (Maggie Baird) is that she is the voice of Samara in Mass Effect 2 & 3," one X user tweeted on Saturday night. Another quickly replied: "WAIT I THOUGHT THIS WAS A JOKE SHE ACTUALLY IS LMAOOOO I F*****G LOVE SAMARA."

Gushing over Justin's performance, Maggie took to Instagram to praise the 'Baby' star, thanking him for making his daughter's childhood dream come true.

"One of the most touching moments ever," she wrote. "It sounds crazy, but we watch our children develop these deep, deep connections to artists who move them, and usually there’s nothing in our power to do.

"But we buy them records and maybe buy them a ticket to a concert (or a movie of a concert in our case, because we couldn’t afford to see an actual concert). I’m so grateful to Justin Bieber for the kindness he has shown Billie."

She added: "And to Hailey who makes so many things wonderful and possible."