They're two of the nation's most adored media personalities, who have forged an unbreakable friendship from their close work ties.
This week as Project host Carrie Bickmore rung in her milestone 40th birthday, radio star Fifi Box made sure her bestie was feeling the love.
WATCH IN THE PLAYER ABOVE: Carrie Bickmore and partner Chris Walker dress up as The Wiggles
On Thursday evening, the mother-of-two took to Instagram to pay tribute to her "ride-or-die sister" with a heartfelt post.
"Happy Birthday my wonderful friend @bickmorecarrie who sets the world alight with her warmth and beauty 💕There is no heart bigger, no mum more devoted, no friend more supportive," Fifi penned.
"You have achieved so much because your tireless dedication and talent is boundless, I can't wait to see what you achieve in the next 40!"
"You are a round-the-clock, always there, ride-or-die sister and here's to another decade of laughs and love my beautiful friend!! 😘😘😘," she signed off the post, which was accompanied by an entire album documenting their many adventures from over the years - from attending red carpets to raising their young children together and enjoying family holidays.
Carrie and Fifi both work on The Project together, with Carrie serving as full-time host alongside colleagues Waleed Aly, Peter Helliar and Lisa Wilkinson, while Fifi is a regular guest host.
The duo both have their own radio shows too, with Carrie hosting alongside comedian Tommy Little on the Carrie and Tommy Show for the Hit Network and Fifi starring in the Fifi, Brendan Fevola and Nick Cody breakfast show on Fox FM.
The pair share another special bond as well, having been able to watch their own daughters also form strong friendships with one another.
Carrie's daughters Evie, five, and Addie, who turns two later this month, along with Fifi's girls Trixie Belle, seven, and Daisy Belle, one, often enjoy playdates together.
The mother-of-three's long-term partner Chris Walker also took to Instagram to pay tribute to his wife by sharing the ultimate throwback video from the time they dressed up as Emma and Lachy Wiggle.
"Happy 40th birthday @bickmorecarrie. I tried to find a photo of your greatest achievement. The Gold Logie, Your OAM, raising millions for @carriesb4bc, raising three kids and the time you retired hurt from the Hopman Cup as a ball girl. I settled on the time we did The Propeller. ❤️," Chris quipped.