Over the years, the Australian actress has both lightened and darkened her natural red locks, however, she had never completely ditched the shade before.
Fans quickly responded to the photo with many noting how different Isla looks. "This is a different person," one wrote. "I didn't even recognise you!!!" another commented.
One person was quick to point out that Isla no longer looks like fellow redhead actress Amy Adams anymore, a comparison that was so frequent Isla once had to tell people that she and Adams were actually "totally different people".
"We have totally different names; hence, we are totally different people," she joked on Jimmy Kimmel, "It's really not that confusing."