The 6-day-old infant is the granddaughter of Princess Anne and the daughter of Zara Phillips and rugby player Mike Tindall. He tweeted her name Thursday, and palace officials confirmed it.
Mia Grace is 16th in line to the British throne.
The 32-year-old Phillips is an equestrian who won a silver medal at the 2012 Olympics. Her father is Capt. Mark Phillips.
