The Duchess of Cambridge was glowing on a trip to the Ealing Studios of Downton Abbey on Thursday.
Wearing a cream coat by British maternity label JoJo Maman Bebe, Kate was taken on a tour of the various departments and met cast and crew.
Her first stop was the hair and makeup trailer, where she chatted to Phyllis Logan, who plays housekeeper Mrs Hughes, as she was prepared for the cameras by makeup artist Nic Collins, 44.
Also in the small space was Rob James-Collier, who plays under-butler Thomas. He pointed at the actress's forehead and joked: "You've come in at a really good point because Phyllis is about to have her botox put in - it's a key point in her morning arrangements."
Moving into the props room, Kate was shown a range of items that feature in the programme, including handwritten letters, newspapers, china and cutlery.
She told prop master Tom Pleydell Pearce: "It's so fantastic, you've got so many objects. There's a lot of attention to detail."
During the tour the Duchess watched a scene being filmed for the latest series - Downton's sixth.
In the dimly lit bedroom of Lady Mary Crawley, played by Michelle Dockery, Kate watched the aristocrat and her maid, Anna Bates, played by Joanne Froggatt, film a scene.
Standing still and surrounded by crew, she watched as Anna helped her mistress dress for a night out.
After they had finished, Kate chatted to the actresses and asked them: "Do you get the giggles?"
They replied in unison: "Oh yes."
The Duchess then joined senior production staff to watch a second take of the scene on monitors outside the bedroom.
Wearing a pair of headphones customised with the initials HRH, Kate looked amazed as executive producer Chris Croucher told her they aim to film just four minutes of screen time a day.
In the servants' hall, she met Brendan Coyle, who plays Bates, alongside the panel of bells used to call staff on the show.
Many interior scenes are filmed in the studios because kitchens and staff quarters at Highclere Castle, where the series is also shot, have been modernised.
Kate said: "You can't tell when you are watching that anything is filmed in a studio."
In the impressive period kitchen set the Duchess found Mrs Patmore, played by Lesley Nicol and Daisy (Sophie McShera) who presented her with a Downton chocolate cake and divulged some show secrets.
The cast members joked about how a fridge in the corner of the room was just a prop. Ms McShera said: "It's got a really bad smell - it's not real."
They also showed Kate how some of the cupboards would not open and joked about food props being used again and again, including a lobster.
Kate, whose second child is due next month, received a number of gifts during her visit including a wooden train for her son Prince George and a bound copy of the script from the first episode of series one, signed by the cast.
The world-wide success of Downton Abbey is all thanks to the Duchess of Cambridge - the show's creator has revealed.
Lord Julien Fellowes told Kate she was the reason the ITV period drama had taken off overseas, after she unwittingly plugged the show during a visit to the US in 2011.
He praised the Duchess as a "functioning member of the Downton team" after she had been taken on an extensive tour of the show's sets at the world famous Ealing Studios in West London.
Kate, who is a fan of the series, clearly enjoyed her behind the scenes visit meeting cast and crew who included Hugh Bonneville who plays Robert, Earl of Grantham and Jim Carter, the one of the leading figure below stairs, butler Mr Carson.
She revelled in the period detail of the costumes, sets and props used in the drama now set during the reign of George V - asking dozens of questions as she visited make-up and hair departments, toured scenery construction areas and watched live filming.
After joining the cast for the group photo in the servants' hall she told the actors: "Thank you so much for letting me into your world."
At the end of the visit Lord Fellowes told the cast, crew and Duchess: "I hope you've seen the pleasure you've given by coming here this morning, we really do appreciate it. It's been rather an extraordinary journey aboard the good ship Downton but this is certainly one of the high points of the voyage."
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