Mary looked stunning in a red, knee-length dress.
The royal chose to pair her look with nude accessories, including a belt and pumps.
Mary also paired her look with some gold drop earrings.
While Mary was attending this year's stamp presentation, husband Prince Frederik was busy in Sydney winding down from this year's Invictus Games.
Sporting a red t-shirt and without his trademark stubble, Frederik posed for a photo posted to the official Instagram account of the Danish royals.
“HRH The Crown Prince was among the first to congratulate Denmark, today, won silver in sailing during Invictus Games in Sydney, Australia,” the Danish palace wrote.
“This week, his Royal Highness visits the multicultural event the Invictus Games, where 25 Danish veterans are attending.
“The idea behind the Invictus Games is to honour injured veterans and thank them for their efforts for their country,’ the palace continued.
“During the eight days of the multisport event, 500 participants from 18 countries will participate.
“In the Danish Invictus Games program, there is also a special focus on personal development, which is to be seen as a contribution to the already ongoing rehabilitation they are taking on."
It's not the first time that Prince Frederik has visited Sydney. In 2013 he and Princess Mary spent five days in Sydney and Tasmanian-born Mary sometimes returns to visit family.