Nicole Kidman has spent the past few months in Australia, and has enjoyed every moment of it.The Undoing star has been able to regularly meet up with her family regularly, including her sister Antonia, who is also her best friend.MORE: Nicole Kidman stuns in sheer dress as she teases exciting news To mark National Sibling Day on Saturday, the Hollywood star paid a special tribute to her sibling, which she shared on Instagram. VIDEO: A look at Nicole Kidman and sister Antonia's incredibly close