They played loving mother and son duo Julie and Ben Rafter on the widely popular Aussie drama Packed To The Rafters from 2008 until 2013.
On Tuesday morning, Rebecca posted a slew of never-before-seen photos with Hugh from their Rafters days, before signing off the sweet tribute as "Mama Bec."
"Happy Birthday to this beautiful son from another Mum. Love you to pieces @hugh_sheridan . Have the most wonderful day! Stay safe over there in the US and can't wait to see you back in Oz soon. Big hugs Mama Bec," Gibney, who is set to step back into the role of Julie Rafter, wrote alongside a collage of snaps of her and Hugh.
In one picture, Hugh and Rebecca can be seen cuddling with to their Rafter's co-star Jessica Marais.
In another photo, Hugh and Rebecca appear to be joking about on the set of the hit TV show as Hugh does the peace sign behind his friend's head.
In a third behind-the-scenes snap, Hugh and Rebecca rub shoulders with co-star Angus McLaren, who played Hugh's on-screen brother Nathan Rafter.
Fans were quick to flood the post with their memories of the show.
"I loved that show ... never wanted it to end. 😭💕," one user wrote.
"Would you believe I have only just started watching Packed to the Rafters! Just started series 2 and loving it! Happy birthday Benno! 🎂🎈," another said, in reference to Hugh's character Ben.
"Miss this family 😘," a third simply said.
The cast of the show have been firm friends for years, with Hugh describing Jessica Marais as one of his "dearest" friends.
While Rebecca and Jess have always shared a very close bond, on and off screen.
"I absolutely love Jess. She's got her struggles, but she'll surprise us all," Rebecca told TV WEEK of her former co-star, who sadly pulled out of the Rafters reboot due to health reasons.
"She's doing really well and I'm in constant contact with her. She is truly one of those unique talents."
In December, Amazon Prime Video officially announced the show's spin-off Back To The Rafters, however production has since been paused due to the COVID-19 pandemic.
The show will be set six years after Packed To The Rafters wrapped.