Fisher was across the pond filming the third season of the half-hour British-American comedy, Catastrophe, which stars Sharon Horgan and Rob Delaney as a newly married couple raising a toddler.
Fisher played Delaney’s TV mother, Mia, and first appeared in the show’s second episode in 2015.
Horgan remembered Fisher, who died at 60 on Tuesday, by sharing a recent photo of the two smiling widely on the Catastrophe set.
“Carrie was my friend. It took me three series but I got her in the end. She was the most generous, fun, gifted, smart, kind, funny funny funny person I've ever met,” Horgan wrote on Instagram. “She certainly wasn't ready to go.”
“I'm so glad we became pals,” she continued. “I'm so devastated at her loss. I want to write about her more but I can't process yet."
Carrie was my friend. It took me three series but I got her in the end. She was the most generous, fun, gifted, smart, kind, funny funny funny person I've ever met. She certainly wasn't ready to go. I'm so glad we became pals. I'm so devastated at her loss. I want to write about her more but I can't process yet.
Fisher had shared the same photo days earlier on Dec. 19, writing on Twitter in her own unique voice: “Sharon Horgan & I pretending we like each other while filming Catastrophe in London.....Succeeding!”
That same day, Fisher posted another candid photo with Horgan and their dogs, including her beloved French bulldog, Gary, as well as a sweet moment with David Cross.
Sharon & our dogs, Gary & Ozzie, doing more pretending.......dogs moving too much pic.twitter.com/vgLrDl8fh0— Carrie Fisher (@carrieffisher) December 19, 2016
David Cross & I ptending we know each other with a jar of something & other stuff..... pic.twitter.com/Lc7dHlPfBl— Carrie Fisher (@carrieffisher) December 19, 2016
One day later on Dec. 20, Fisher snapped a photo with a fan on the streets of London outside the Salvador Dali Museum looking healthy and happy.
Alongside photos of Fisher sightseeing that same day, Fisher -- who was reportedly promoting her book, The Princess Diarist -- joked about her cameo in Rogue One: “Gary heard I do some of my best work in it.”
In Bruges looking for a theater ✝️🏨🅰✝️💲. 🅿️🕒🅰✌🏼ℹ♑️g. ®🅾️g⛎📧. 🅾️♑️📧..g🅰®✌🏼. 🏨📧🅰®d. ℹ. D🅾️. 💲🅾️Ⓜ️📧. 🅾️f. Ⓜ️✌🏼 🅱️📧💲✝️. 〰🅾️®k. ℹ♑️. ℹ✝️ pic.twitter.com/nzVlYv2bi6— Carrie Fisher (@carrieffisher) December 20, 2016
Fisher’s last tweet on Dec. 21 was a photo outside of the Charles Dickens Lounge.
"🅿️📧🅾️🅿️🕒📧have🅰g📧D soⓂ️⛎©♓️Ucant even GET THEM 2 DOⓂ️🅾️✝️ℹ🅾️♑️©APTURE"-as ✝️♓️🅾️these folksR disobedientAuditions R held.Gary didnt get©🅰💲✝️ pic.twitter.com/RuEdx1AUIW— Carrie Fisher (@carrieffisher) December 21, 2016
Earlier this year, ET spoke with Horgan about the chances of moving Catastrophe from its U.K. setting to the U.S., as well as Fisher’s pivotal role on the show.
"We’re very in love with Carrie Fisher, so we always try and think of how we can get her in it more. So, obviously, heading back to Rob's hometown would give us more time with her,” Horgan told ET back in August. “And so it is a little bit of, it's something we can confer for a lot of reasons. But, you know, hopefully at some point it'll happen."
During a Tribeca Tune-In event in April, Fisher explained why she was interested in playing an “awful mother” on Catastrophe.
“I did really want to play an awful person," Fisher said. "There are not a lot of choices for women past 27. I don’t wait by the phone.”
Amazon, which streams Catastrophe, also paid tribute to Fisher on Tuesday.
“It is with a very deep sadness that Billie Lourd confirms that her beloved mother Carrie Fisher passed away at 8:55 this morning,” family spokesperson Simon Halls said in a statement to ET on behalf of Fisher’s daughter, Billie Lourd, on Tuesday. “She was loved by the world and she will be missed profoundly. Our entire family thanks you for your thoughts and prayers.”
For more on Fisher’s death, watch the video below.
Additional reporting by Stacy Lambe.