THE Duke and Duchess of Cambridge have named their third child Louis Arthur Charles.

The baby will be known as His Royal Highness Prince Louis of Cambridge.

Kensington Palace made the announcement on Friday morning, four days after the birth.

It is the longest we have waited for a royal baby name in years - Prince George and Princess Charlotte's names were announced two days after their births in 2013 and 2015.

Louis is French and means ‘famous warrior’ from the Old German ‘Chlodovech’.

The new prince was born at 11.01am on Monday, weighing 8lb 7oz at the Lindo Wing of St Mary’s Hospital in London.

He is fifth in line to the throne.

The names honour both the Prince's grandfather, Prince Charles, and Louis Mountbatten, the Duke of Edinburgh's mentor who was killed by an IRA bomb in 1979.

His older brother, Prince George of Cambridge, and his father Prince William both have Louis as middle names.