In an emotional tribute, Sam shared a special message for her Survivor super-fan sibling.
"Despite never smiling in photos.. you are hands down the biggest legend with the softest and kindest soul," Sam wrote on Instagram. "Everyone who meets you can see and feel the magic within you.
"The worlds Number 1 Survivor super fan finally got a chance to play... only to get injured day 1. But you still gave it your all. You played with authenticity, integrity and heart," she continued.
"I’m incredibly proud of you. Hopefully, you can get your body in tip-top shape, and get a chance at redemption one day. I’m going to miss seeing your cute little head on the screen. You’re a superstar in my eyes. Love you so much bro. Thank you to the Water team for taking him under your wings."
Alex's co-stars including Khanh Ong and Mark Wales also shared their condolences, acknowledging how tough it would have been to withdraw from the game. While Sophie Cachia wrote her own lengthy tribute.
"This was horrible. A genuinely gorgeous guy who couldn’t do it anymore,” Sophie wrote on Instagram.
"I felt for Alex terribly that he left the game that way, and then had to go back to camp with such guilt that I was still there and he was gone. He was loved by EVERYONE, such a loss around camp and the game.
"I didn’t get much time with you – but in the time I did – you’re a legend and I admire you so much for making that call on your own terms. Nothing but respect. Off to face another day."
Australian Survivor: Blood V Water sees "family members" of varying degrees signed on together, with Alex competing with his sister Sam's boyfriend, Jay Bruno.
"I had to have someone that was close to family and at the time he was,” Jay explained to Sydney Confidential of competing with Alex.
However, since filming Survivor, Jay and Sam have gone their separate ways. But it seems the boys are still good mates.
With Alex now out of the game, it's up to Jay to win for the pair.
This story originally appeared on our sister site, WHO.