The "dark-haired woman" was spotted pushing Prince George around London's Hyde Park in a pram recently, according to UK edition of HELLO! magazine.
The Spaniard who has been working and studying in the UK for the last 20 years is currently being trained for the role by Kate's mother Carole, according to the celebrity magazine.
"She has worked with other prominent high-society families in the past," a friend of the unnamed woman said.
"She is not married and doesn't have a boyfriend as her life is totally dedicated to the family she is working with. She is known for being totally professional — married to the job," the friend said.
The Spanish Mary Poppins is expected to help look after the Queen's great-grandson when his otherwise "hands-on" parents are busy with professional engagements in Britain and overseas.
It appears UK Prime Minister David Cameron's current anti-immigration push hasn't affected the British royals choice of a Spanish nanny, noted Spanish national El País in an irony-laden piece on the news.