Kate Middleton has been admitted to hospital in the early stages of labour.
Kensington Palace's official Twitter account said she had been taken to St Mary's Hospital in Paddington, London, on Monday morning (local time).
The Duchess of Cambridge is expecting her third child. She gave birth to Prince George in 2013 and to his sister Princess Charlotte in 2015.
Both children were also born in St Mary's Hospital.
The 36-year-old announced her most recent pregnancy in September 2017.