It's been an emotional morning for the cast of Call The Midwife. Firstly, they were greeted with the happy news that Ben Caplan, who plays PC Noakes in the nostalgic nursing drama, spent the previous day in hospital, while his wife gave birth to their second child.
"The midwives were amazing for what they did," says Caplan who works closely with Miranda Hart in the well-loved series, who plays his frightfully posh but all round good egg of a wife, Chummy.
"It adds to my respect for the show we make, for celebrating the midwives and what they do, because they do an amazing job," he adds.
Then, after a round of congratulations and well wishes, the show's stars huddle together to watch the "heart-rending" first episode of the fourth series, which starts in January, preceded by their annual Christmas Day special, of course.
"Did you not hear us sobbing?" teases Helen George, who has played fun-loving Trixie since the show began in 2012.
"I'm trying to keep the tears from coming out so I don't spoil my make up," adds Pam Ferris, who depicts the blunt but caring Sister Evangelina. "It's very moving."
As it transpires, Ferris is not the only one who wells up in her household when watching the show. Indeed, she's expecting full waterworks when her husband sees this year's Christmas special, which flashes forward to 2005 and sees narrator Vanessa Redgrave make her first screen appearance as the older Jenny.
As Jenny reminisces about her time at Nonnatus House, the episode cuts back to 1960, where the nuns and nurses are preparing for a busy Christmas. Chummy's choreographing the festive concert, Trixie's designing a Father Christmas outfit for Fred and Cynthia's embroiled in a case concerning two former residents of a Victorian mental hospital.
"My husband cries a lot," says the veteran actress, who adds that her free-flowing tears make watching the Christmas special like "looking through a fishmongers' window".
"It's industrial strength kitchen roll he requires, not tissues," Ferris (66) continues. "Usually he is very helpful with things - he likes to listen to my lines and helps with stuff, but on this particular show, he says, 'Don't tell me, don't spoil it for me'."
Under heavy restrictions from the show's publicists, the storylines are closely guarded, so Ferris' husband is quite safe.
And even though the stars know the ins and outs of the Christmas Day special, which was actually filmed during a scorching heatwave in the summer, they all readily admit that they'll be tuning in on December 25.
"I'll definitely watch it, but I will record it as well," says Cliff Parisi (54) who plays handyman Fred, and whose wife is also expecting a baby in the New Year.
"But you know what it's like on Christmas Day," he adds, explaining that to get everybody's attention, he'll probably be saying things like: "'You've all got to watch me! This is my bit. I'm going to rewind it if you talk again! Stop rustling that wrapping paper'."
Last year, the show beat Downton Abbey in the Christmas Day ratings war, with a sizeable 7.1m viewers tuning in, and managed to pull in a hefty 10m viewers in 2012.
Despite this, the cast are still surprised at how quickly the show has become a classic.
"When we did our second Christmas special, the press reviewed it as if we'd always done it," says Ferris. "I think that's something to do with the historical nature of the show, people feel like it was always there."
Parisi adds: "People used to just talk about Coronation Street at Christmas, but now they talk about Coronation Street, EastEnders, Downton Abbey, Call The Midwife, Doctor Who as well. And it's nice to be in that list."
Although Jessica Raine, who played central character Jenny, left at the end of this series, the cast are convinced the fourth series will still be a belter, even if her absence is sorely missed. "I remember my first day on set without Jess, and I was sort of in mourning," says George. "I felt like I was walking around an old distant memory, like when you've gone back to school after you've left, and none of your friends are there."
But while Bryony Hannah, who plays sweet-tempered nurse Cynthia, admits they all miss their friend, they have a "light" in the "wonderful" Charlotte Ritchie, best known for her role as posh student Oregon in Fresh Meat, who has joined the line-up as nervous newbie Barbara.
"The series is in a really good place," adds George. "It's really strong, we're all proud of it."
And with a fifth series commissioned before the fourth has even been on air, the cast and BBC seem to have plenty of confidence in its future. Although it's "impossible" to answer, the actors have their own theories on why Call The Midwife has been such a hit.
"A viewer said to me how much they absolutely adored the show," says Judy Parfitt, who plays eccentric Sister Monica Joan. "They said it's also those things that are subliminal. It's not banged on the head. It doesn't give you a lecture, it's just presented. I think that's one of the great things about the show."
For Ferris, who says she and Parfitt - who were alive during the Fifties and Sixties - sometimes "supply memories" for their colleagues, the series serves as an important reminder to appreciate all we have.
"I think it's really healthy, politically, to remember how brilliant our National Health Service is," she says.
"Because, you know, we complain it won't do this, that and the other for us, but when you think how it started and how vital it was then, and how we are in danger of taking it for granted, it's really important to remember that."