In an interview with Glamour magazine, the feisty actress said Bear was going to grow up a Winslet – and not a Rocknroll, the surname her husband Ned adopted. The 38-year-old actress said: "We haven't ever really had that conversation; it was always going to have my name. Mia and Joe have it as part of their name, so it would be weird if this baby didn't."
Then she blasted: "Of course we're not going to call it RocknRoll. People might judge all they like, but I'm a f**king grown-up."
Her husband of one year was born Ned Abel Smith, but changed his surname to Rocknroll via deed poll in 2008. Mia Honey, 13, is the daughter of Kate and her first husband Jim Threapleton, while Joe Alfie, 10, is the son from her second marriage to director Sam Mendes.
Aside from discussing her new baby, Kate also talked about her lack of concern about losing her pregnancy weight in order to regain her pre-baby figure.
Dismissing the concerns, she said: "Having just had a baby, I'm not going to be thinking about my a**e."
• The full interview appears in the February issue of GLAMOUR, on sale now.