Reports in a number of European publications have been speculating about the pair's relationship since an article ran in a Madrid newspaper in the weekend.
In an story published on Saturday, Spanish national daily newspaper ABC reported that the reason the Princess was not at her husband Prince Albert II's side at the coronation of Willem-Alexander in the Netherlands two weeks ago was because she was in her native South Africa with rugby star Byron Kelleher.
Ex-Olympic swimmer Charlene, 35, is in South Africa working with her sports-focused charitable foundation Princess Charlene of Monaco Foundation, for which Dunedin-born Kelleher, 36, is in charge of rugby projects.
While there is no evidence that the two are having an affair, ABC said speculation was mounting.
"Rumours about a relationship between the two have erupted," the article said.
ABC said Kelleher, who they described as an "intimate friend," also showed up at the Princess' side at a tennis tournament in Monte Carlo.
A number of other European sites are reporting the rumours, with headlines like "Charlene of Monaco and rugbyman Byron: An affair in the works?"
Former All Black and former teammate for the Highlanders Josh Kronfeld said he hadn't heard anything about the reports, but said it "wouldn't surprise" him.
"If anyone can meet women, it's him," he said. "I wouldn't be surprised. If anyone could do it, it'd be Byron Kelleher."
Princess Charlene's camp is staying silent on the issue.
It's not the first time the pair have been spotted hanging out together. The Diary reported in June last year that the was spending time at the Monastero Santa Rosa with the Princess and her husband on Italy's Amalfi Coast.
Kelleher and Charlene swam laps in the infinity pool overlooking the cerulean Bay of Salerno.
Kelleher also attended the royal couple's wedding in 2011.
- by Cassandra Mason, nzherald.co.nz
