Inside Fergie's Awkward Moment at the TrevorLIVE Gala: 'It Was a Gag That Fell Flat' Says Rep

Fergie pulled a Kanye West Sunday night, leaving some members of the audience scratching their heads after an off-script stage crash at the TrevorLIVE Gala in L.A.

At the star-studded fundraiser for the Trevor Project — a nonprofit that works to prevent suicides among LGBTQ youth — Fergie sat with honoree Tom Ford, Isla Fisher and actor Armie Hammer, who presented the award to the designer and Nocturnal Animals director.

As E! News first reported, Fergie joined Hammer onstage, interrupting his speech as she pretended to be the actor. The crowd looked on in surprise as she delivered a few bars of her new ballad “A Little Work,” telling the audience: “This is not a shameless promotion.”

“It got awkward fast when everyone realized this wasn’t planned,” an observer tells PEOPLE. “Everyone in the room was uncomfortable as she rambled on and sang into the microphone.”

However, a rep for Fergie says the stunt was simply a well-intentioned, albeit ill-timed, joke, telling PEOPLE: “It was a gag that everyone at the table came up with that fell flat due to timing.”

Later in the evening, the former Black Eyed Peas star unexpectedly returned to the microphone before singer Shoshana Bean’s performance.

“Give it up for Tom Ford! Trevor Project! This project. I wasn’t even planned to speak tonight, but I guess I can’t stand it when everyone else is up here singing,” Fergie reportedly said.

Hammer’s wife, Elizabeth Chambers, made light of the incident on social media that same night.

“Our table was the fun table. Congratulations, Tom Ford for receiving the @trevorproject HERO award and to @armiehammer for graciously presenting it to the man who does it all. And to @Fergie for the assist,” the mother of two captioned a photo of her and Fergie.

After news of her antics broke, some fans expressed concern on social media over Fergie’s behavior.

“She’s happy and healthy,” her rep says of the singer.

RELATED VIDEO: Fergie Reveals ‘It Was Getting a Little Weird’ Pretending to Still Be with Josh Duhamel Before Going Public with Split

In September, Fergie and husband Josh Duhamel announced they had recently split in a joint statement provided exclusively to PEOPLE; the couple continue to coparent 4-year-old son Axl Jack.

“A separation is hard for anyone, but she’s doing really good,” adds the rep of Fergie, who released her sophomore album Double Dutchess this fall and will host Fox’s new singing competition, Four. “She’s 100 percent focused on Axl while also working incredibly hard.”