According to E! News, the handsome couple are expecting their second baby, and let slip the news at the Hollywood premiere of Doctor Strange last night.
Walking the red carpet at the historic Chinese Theatre on Hollywood Boulevard, Sophie, 38, looked stunning in a strapless, flowing gown.
This would be the second pregnancy for the happy couple, who welcomed baby Christopher (known as Kit) in June 2015 four months after they tied the knot on Valentine's day.
The Sherlock star, 40, spoke about his experiences of fatherhood in an interview with Vanity Fair earlier this year.
"Having a baby – it's massive," he said. "And on a very unexpected level. Suddenly I understood my parents much more proudly than I ever had before."
He said that welcoming little Kit allowed him to better prepare for his role as Hamlet at London's Barbican Theatre. "I was expecting with Hamlet that it might be a hindrance to be a father, because it's all about being a son," he commented. "But it's the opposite. You understand much more about being a son, becoming a father."
The impact fatherhood and marriage has had on Benedict is very apparent to those around him. Tilda Swinton, who co-stars with him in Doctor Strange, spoke with admiration for the new dad and husband to the publication.
"My fondest impression of him is as a new husband besotted by his girl, and a new father enchanted by his boy," she said. "I think he knows what he wants – and has – a life first and foremost, that his life suits and nourishes him and that it makes the world go round."