Duchess Catherine reportedly wanted sister Pippa Middleton to be her lady-in-waiting but the Palace felt it would be better to put an official in the role.
The 30-year-old Royal - whose husband Prince William is currently completing a tour of duty as a Raf search and rescue helicopter pilot in the Falkland Islands - is said to have wanted her younger sibling close by to keep her company.
But a source claims the powers that be at Buckingham Palace felt it would be best to avoid mixing business and pleasure.
The insider told Now magazine: ''They thought it was better to have an official in the role, especially as Pippa attracts so much media attention and is writing her party planning book.''
But the report claims the 28-year-old socialite - who gained overnight recognition as Catherine's maid of honour at her April 2011 wedding to William - would have been able to provide support for her sister during his absence.
The source said: ''Kate calls her sister her ''right hand'' and feels relaxed in her company.
''Pippa is key to Kate's happiness. It's a stressful, lonely job being a Royal and Pippa would've helped to build Kate's morale while Wills is away.''