The power of Chinese whispers shouldn't be under-estimated after a family relative revealed that the Heffernan's new baby was a whopping 12lb and the rumour spread like wildfire.
Many fans of the Rob and Marian took to social media to congratulate the couple for the happy event and to reveal their astonishment at the size of newborn baby girl.
When the world gold medallist realised that the wrong information was being circulated he clarified that his bouncing baby girl was a more normal sized 8lb.
The 35-year-old admitted he was "over the moon" with the safe delivery of his new baby daughter after his wife and coach, Marian, had been in labour for almost 25 hours.
The little girl was born just after 4pm yesterday in Cork University Maternity Hospital (CUMH).
The couple still haven't decided on a name for their new arrival but will now take suggestions from Rob's two children, Cathal and Meghan. "It's brilliant ... I am absolutely thrilled. It caps a wonderful year for us all," Rob said.
Marian went into labour on Saturday afternoon as Rob was about to start a gruelling training session. The couple rushed to CUMH and, unlike her speedy dad, the little girl was in no rush to be delivered. At one point, Rob joked via Twitter that he was now ready for an epidural.
"I have a new baby daughter and I am so proud of my wife Marian and the staff at CUMH," he said.