Prince George and Princess Charlotte have a new cousin after the birth of a second daughter for Lord Frederick Windsor and his wife, actress Sophie Winkleman.

Lord Windsor is the son of Prince and Princess Michael of Kent, who said: "Lord and Lady Frederick Windsor have this morning announced the birth of their second daughter, Isabella Alexandra May Windsor.

"The baby was safely delivered at 11.59pm on 16th January 2016 at Chelsea & Westminster Hospital.

"Her Majesty the Queen has been informed. Prince and Princess Michael of Kent's family and Lady Frederick's family are delighted with the news."

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Prince Michael is the first cousin of Queen Elizabeth II, which makes baby Isabella a third cousin to William and Kate's children.

The couple's first child, daughter Maud, was born in August 2013 in Los Angeles.

Winkleman, 35, who has starred in the TV sitcoms Peep Show and Two and a Half Men, married Lord Frederick, 34, in September 2009, at Hampton Court.

-AAP