Simon O'Malley, Headmaster at Thomas's Battersea echoed the family' excitement.
He said: "We are delighted that The Duke and Duchess of Cambridge have decided that Princess Charlotte will join her elder brother, Prince George, at Thomas's Battersea."
"We greatly look forward to welcoming her and all of our new pupils to the school in September."
That's not the only family connection at the school.
Charlotte will find a friend in fellow pupil, cousin Maud Windsor - the five-year-old daughter of Lord Frederick Windsor and Sophie Winkleman.
She is in the same year as George.
Thomas’s Battersea describes itself as a Christian school.
They are open to children of all faiths and believes in “praise as the greatest motivator”.
Parents are told their children will be in an atmosphere which seeks positive relationships between pupils, teachers and parents.
George, who is six, started at the school in September 2017.
Art, ballet, drama, ICT, French, music and physical education are all taught by specialist teachers from a child’s first day.
The school is housed in a Grade II listed building, the former Sir Walter St John’s Grammar School which dates back to 1700.
In the past, William said his son “absolutely loves ballet”.