It's singer Brian McFadden and model Ruby Rose who revealed the presence of those lovebirds in Australia.
"Having dinner with Mila Kunis. As you do," the 32-year-old singer tweeted. "I'm having dinner with Mila Kunis and Ashton Kutcher. I will have to see her in London!" Ruby also tweeted.
Later, Ruby posted a photo on Twitter account with a caption, "dinner last night.. Everyone's hall pass... And Ashton."
It's still unknown how long the duo will stay in Sydney. Kutcher is currently taking a break from filming Two and a Half Men, while Kunis will have some movie projects in the near future.