The Titanic actress and husband Ned Rocknroll became parents to a baby boy on 7 December and have now released his name: Bear Winslet.
Bear was born at an NHS hospital in Sussex weighing 9lbs. No further details have been released.
It's Kate's third child but her first with businessman Ned. She is also mum to Mia, 13, from her first marriage to Jim Threapleton, and son Joe, ten, from her marriage to Oscar-winning film director Sam Mendes.
She married 34-year-old Ned Rocknroll - the nephew of Sir Richard Branson - in a private ceremony in December 2012 following a summer engagement.
Last year, Kate revealed she'd told The Queen nothing in her life was as important as motherhood.
While accepting a CBE for services to drama, she was asked by Her Majesty if she enjoyed acting. "I said yes, I liked it, but not as much as being a mother," said Kate. "She said, 'It is the best job.'"
More celebrities who welcomed babies in 2013 below!
Copyright: Love & Lust London