“It was a lovely opportunity to move the huge body of research that I’d built up over the series and the films to incrementally push forward again into this new decade and look for the very cutting-edge shifts that were taking place [in fashion] and to mark them in the film,” said costume designer Anna Robbins, who is bidding farewell to the franchise with the premiere of “Downton Abbey: The Grand Finale” on Friday.

The film marks the final chapter in the Julian Fellowes-created drama, which began as a series in 2010. The Emmy Award-winning show quickly became a global phenomenon, chronicling the upstairs-downstairs lives of the Crawley family and their staff in the early 20th century, through World War I and into the roaring ’20s. The series spawned three films throughout the years.

For “The Grande Finale,” Robbins wasn’t only tasked with sending off the beloved characters in style, she also introduced a new decade for the Crawley family’s fashion to embrace. “There were some significant sartorial changes that were taking place within womenswear and within menswear to an extent. It was about finding them and showcasing them within the film,” she said.

From the beginning of “The Grand Finale,” fashion reigns supreme. The reintroduction of Lady Mary Talbot, formerly Crawley (Michelle Dockery), features the aristocrat in a striking, red sleeveless gown, inspired by designs from the 1930s and infused with certain contemporary elements. The dress was a bespoke piece designed for the film, featuring Art Deco vintage jewelry pieces.

“That still meant that it felt like it was really anchored in the early ‘30s and this really exciting step that was taking place with the advent of the bias cut,” Robbins said.

The creation of the bias cut is credited to French couturier Madeleine Vionnet (1876-1975), who championed the design in the 1920s, eventually gaining widespread popularity by the ’30s. The bias cut is defined as “a technique of cutting across the grain of a textile to produce a carefully draped silhouette which clung naturally to the body,” per the Victoria & Albert Museum.

The rise of the bias cut was a silhouette on which Robbins wanted to focus, imbuing the fluid style with elements of luxury and glamour intrinsic to the aristocracy. “I’d found these original pieces of lamé, this sort of silver lamé with this print on it [of] silver, turquoise and coral,” Robbins said of the costume worn by Lady Edith (Laura Carmichael) in the ballroom scene early on in the film.

In just one scene, Robbins’ incorporated “vintage velvet, vintage lace, vintage lamé,” that were “all kind of brought together with other contemporary silks” to create continuity and belief that these pieces were indeed from the Crawley wardrobe.

“My approach with ‘Downton’ specifically but generally with a period piece is to try to anchor it in the time as much as I can. I think using original pieces and vintage from that time is that anchor. It really kind of pulls it into where it’s set,” the costume designer said of her process.

“I would shop for originals, I would go to vintage fairs, contact vintage traders I’ve got connections with and shop for garments that were beautiful — almost 100 years old in amazing quality. But equally I would be looking for fabrics and trims and bits of beading and bits of embroidery, buttons — all the little bits and pieces that could then be incorporated into a bespoke new make. It was a combination of customizing originals, taking something that’s not quite right or is starting to fall apart in bits and use it to make something new.”

As with the previous two films and the series, Robbins’ costume designs served as an extension of the characters. “The clothing has to be right for who they are and what their station is — their class, their position, all of that. It speaks of who they are in that respect, but it also talks of their personality and their emotional state, whether they’re feeling happy or sad, or confident or vulnerable,” she said.

Color, texture and small details like patterns and sartorial motifs clue the audience further into a character’s interiority. “With Mary, typically there would be something graphic about her costumes or something quite linear, there would be a lot of colorblocking, it wouldn’t be soft and pretty,” Robbins said.

“But then there’s aspects of Mary across the films, definitely in this film, where there’s a real vulnerability and we’ve introduced really delicate little floral patterns in the lace, but it’s not a big bold frivolous pattern, it’s a pattern that makes sense for who she is,” Robbins explained.

The costume designer has spent roughly one decade with the ensemble of characters. Over the course of her time with the fictional Crawley family and those who work in service at Downton, Robbins’ curated tableaus of visual harmony from scene to scene and dynamic juxtapositions between individual characters’ intentions and personalities through her costuming.

“It has been an absolute pleasure and a privilege to work with such talented, wonderful people,” Robbins said, reflecting on her time with the production. “We have become a family in front of and behind the camera. It’s my ‘Downton’ family! I think we will feel bonded forevermore.”

The final chapter of “Downton Abbey” threads together the grandeur of the costumes and settings, along with the characters longtime fans have come to know and love for one last exercise of opulent escapism. Robbins, with the cast and creative team, steps away from the “Downton Abbey” universe dressed in gratitude. “It’s a really fitting farewell.”