The Trainspotting star’s eldest daughter, Clara, revealed the news on her Instagram account on the 27 June. "Welcome to the world little brother.
Congratulations to my Dad & Mary - this is the greatest gift," wrote Clara, 25, alongside two pictures of her holding her newborn brother.
It is understood Winstead, 36, had not been photographed publicly with a baby bump and the couple had managed to keep the pregnancy a secret.
McGregor’s daughter Esther, 19, also shared a post on social media, revealing the baby’s name as Laurie. Her message read: "Met my little brother looking like a pirate.
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