Sarah, who played Mandy Richardson in the long-running Channel 4 soap, welcomed her son with boyfriend Jonathan Smith and announced the news on Instagram.
Posting a snap of bunting, which read 'It's a boy', Sarah told her followers that she and Jonathan are completely smitten with their little bundle.
She said: "Our gorgeous little man arrived safe & well on 7 August. We're in love."
Sarah, 34, joined the cast of Hollyoaks aged just 14 in 1996 before leaving the soap in 2006. She later returned for several guest appearances.
More recently, Sarah appeared as charity worker Taylor Ashbie in BBC One's Casualty.
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