The birthday girl herself, Carole, who turns 60 on 31 January, was spotted at Gatwick airport on Monday with Kate's dad, Michael Middleton, flying out to join the young royals in paradise.
Kate and Wills flew out to St Lucia last Thursday, before transferring to Mustique on a private plane.
The young family flew first class on British Airways, where, according to the Express, fellow passengers said Prince George behaved impeccably.
It is believed Kate's brother and sister, James and Pippa Middleton, will also be joining the group for the annual Mustique getaway.
According to Hello! magazine, the family are thought to be staying at the luxury Aurora Villa, which boasts a chef and housekeeper, a 45ft private swimming pool and sundeck, and a reported price tag of over £13,000 a week.
Mustique, with its talcum powder-white sands and turquoise sea, has long been a draw for the rich and famous, with Mick Jagger famously owning a home there.
It will be the perfect opportunity for Kate, who is six months pregnant with her second child, to relax.
She has been busy fulfilling a number of public engagements recently, including a visit to Kensington charity Family Friends, celebrating the work of foster carers at the Fostering Network event, and a trip to the Barlby Primary School in Ladbroke Grove, which was her public first engagement of 2015.
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