Back at the height of Kate Gate, rumors of an affair with Prince William resurfaced. These rumors came before the public knew about Princess Catherine. There was no evidence of any romantic relationship, and Rose denied the claims through her lawyer.

These rumors added an awkward twist to one of Catherine's previous code names. According to Andrew Morton's biography, "William and Katherine," they went by the names Martin and Rose Middleton during a trip to the Seychelles in 2007. This trip came after they reconciled after a brief separation. Marsha Moody notes in her book that the couple spent a wonderful week rekindling their romance away from prying eyes.

The choice of "Rose" as a nickname is particularly ironic given the rumors. In 2018, cheating rumors resurfaced, claiming that William had an affair with Rose while Kate was pregnant with Louis. When confronted, William reportedly laughed off the accusations, claiming that there was no truth to them. His lawyer called the allegations false and damaging. Rose was the only one to publicly address the rumors.

Catherine also used other fake names when traveling with William. Robert Jobson notes in his book Katherine the Princess of Wales that in the early 2000s, they would check into hotels under the names of Mr. or Mrs. Smith, which probably didn't fool anyone. This was before the film of the same name came out, so they weren't joking about their secrecy. In 2001, William sometimes used the name Steve, which Jobson described as a rather sad attempt to keep a low profile.

Catherine has her own funny nicknames for William, like "Baly" and "Big Willie." An insider revealed that William would playfully refer to Kate as “The Duchess of Dittle,” poking fun at her more laid-back royal schedule, which is often shortened to DOD. While these royal nicknames may seem funny, they’re meant to help them discreetly identify each other. There may be more secret names that only they know, but it seems “Rose” for Kate has been a given.