The magazine suggested that Bec had been spending an increasing amount of time with an American trainer named Mark.
Bec and husband Lleyton were quick to deny the reports and revealed that Bec's mystery man is actually her brother, Shaun Cartwright.
"For some time now we've had to endure fictional, rubbish stories by New Idea...targeted at our marriage, private lives and even work with charities," the couple said. "This brazen fabrication by New Idea will hopefully highlight to the Australian public the untruths and lies some magazines will resort to to achieve increased sales."
When approached for comment, a spokesperson for Pacific Magazines, publisher of New Idea, said: "An error has been made concerning the identity of an individual.
"New Idea apologises for this mistake and will address it."