The actor shared a photo of himself, Brooks, his brother Chris Hemsworth along with Chris's wife Elsa Pataky and Matt Damon's wife, Luciana Barroso, in attendance at the Gold Dinner 2021, held at Sydney Airport in Australia.
"Fantastic night raising much needed funds and awareness for one of the most important and challenging issues, children's mental health," Liam, 31, wrote in the caption.
The group dressed to the nines with the Hemsworth brothers donning suits while Pataky wore a bejeweled white dress, and Brooks, 23, and Barroso, 45, wore black dresses.
In May, Hemsworth appeared in a photo slideshow shared by Brooks' friend Michele Merkin as she wished the model a happy birthday.
The Hunger Games star photobombed his girlfriend as they were photographed with a group of friends.
Hemsworth and Brooks were first spotted together in December 2019 at a brunch with the actor's parents, Craig and Leonie, in Byron Bay, New South Wales, Australia.
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Since then, the two have been spotted out together frequently, kissing on a beach in their home country, enjoying casual Malibu dates during a trip back to America and spending quiet nights at home playing Scrabble games while staying in amid the coronavirus pandemic.
Late last summer, they were photographed enjoying a hike to the Byron Bay Lighthouse, walking barefoot as they headed toward their destination.
"Liam and Gabriella have spent a lot of time in Australia together," a source told PEOPLE of the duo in January 2020, adding at the time that they were "getting serious."