Actress Amanda Seyfried's partner has revealed that they married in secret at the weekend.

The Hollywood star, who is expecting her first child with fellow actor Thomas Sadoski, became engaged to him in September last year after around six months of dating.

Sadoski, who starred in Aaron Sorkin's acclaimed HBO drama The Newsroom, appeared in the 2015 film The Last Word with Seyfried, revealed that they eloped last Sunday.

During an appearance on The Late Late Show with James Corden, Sadoski flashed his left hand to reveal the wedding band on his third finger.

A stunned Corden said: "I didn't know you got married. When did you get married?"

Sadoski revealed the day they married, and added: "We eloped, we just took off into the country with an officiant, just the two of us, and did our thing."

He said: "Listen, she's the person I love, admire, respect most in the world. I know you guys are close friends and I know that she would want you to know, so keep it quiet, don't tell anybody."

As Corden and fellow guest, actress Vanessa Hudgens, congratulated him, the audience whooped and cheered.

"It was beautiful, it was everything that it should be," Sadoski said, describing the ceremony. "It was the two of us talking to each other."

During the interview, he was asked if he was ready for his first child with Mean Girls and Les Miserables actress Seyfried. "How can you be?" he joked.

"I'm more excited about this than I've ever been about anything in my entire life, and I'm also more terrified about it than anything I've ever been in my entire life."