"Downton Abbey" welcomed a royal visitor Thursday — and the TV show's creator told the Duchess of Cambridge she's partly responsible for its global success.

Kate visited the set of the award-winning costume drama at London's Ealing Studios, meeting cast members including Jim Carter, who plays butler Mr. Carson, Lady Mary actress Michele Dockery, and the show's Lord and Lady Grantham, Hugh Bonneville and Elizabeth McGovern.

The duchess visited hair and makeup departments, toured scenery construction and watched a scene being filmed for the show's upcoming sixth season.

The show's writer, Julian Fellowes, told Kate that "your Royal Highness has played a significant part in the 'Downton' story already."

Fellowes described how a 2011 visit to the U.S. by Kate and her husband, Prince William, came as producers tried to raise the profile of the show.

Fellowes said when the duchess mentioned she was a fan "this went into the media like an Exocet missile. And soon all of America and most of the world knew it."

The tour was one of Kate's final public engagements before she is due to give birth to her second child next month.