Fans immediately jumped to the post, needing to know if the bump was in fact real.
'IS IT REAL😍,' one eagerly asked, with another adding, 'I screamed SO loud because I honestly believed it was real'.
Several other commenters just wrote 'Congratulations.'
The Aussie actress even fooled fellow Home And Away star Lynne McGranger, who wrote: 'Congrats guys, how exciting!'
Rebecca, who has been married to fellow Home And Away alum Luke Mitchell since 2013, then uploaded another picture of her alleged 'bump', verifying that it was in fact fake.
She wrote, '100% melon for my upcoming film #SLAM.'
Lynne McGranger responded, 'Well congratulations on your watermelon 🍉! Doesn’t have the same ring to it does it 😂'
Other fans wrote, 'Wow, you got me good!' and 'Looks so real haha! Love it!'