"I will so miss you. I already do," the actress wrote in a tribute on Instagram

Shannen Doherty is paying tribute to her late best friend and stylist Deborah Waknin-Harwin.

In an Instagram post on Monday, the actress, 48, reflected her nearly three-decades long friendship with Waknin-Harwin, sharing photos of them together as well as a touching homage about how the fashion stylist was “a constant” in her life before her recent death.

“Around 28 years ago when I met Deborah, she made me squeeze into very tight red patent pants. It was an instant friendship. A friendship that in 28 years has endured, grown and been cherished by us both,” she began her post. “She taught me to play backgammon. She introduced me to the island of ST. Barth which started our girl trips there. She taught me that when she dressed me, I looked better lol.”

According to Doherty, they were together “thru boyfriends and husbands” as well as “[d]ivorces, tears and laughter.”

Shannen Doherty
Shannen Doherty and Deborah Waknin-Harwin
| Credit: Shannen Doherty/Instagram

“We danced on tables (and fell off them- inside joke) all around the world together,” she wrote. “I was her maid of honor at her wedding to the love of her life Craig. We cried when she called to tell me she was pregnant with her extraordinary daughter Olivia.”

Doherty, who revealed last month that her breast cancer had returned, said that she and Waknin-Harwin were also there for one another during their respective cancer diagnosis.

“We worked on shows together. We grew up…. together. She was a constant. Thru my cancer and I for her when she got diagnosed 4 years ago,” she shared. “She smiled, a lot. She radiated beauty, intelligence and goodness. She was and is wedged into my heart so deeply. We were more than best friends. We were sisters. Tied to each other by the universe, by our very essences that recognized each other instantly.”

Shannen Doherty
Shannen Doherty and Deborah Waknin-Harwin
| Credit: Shannen Doherty/Instagram

Doherty ended the tribute with a message to her late friend, writing, “Deb I hope you are dancing on tables again, having a tequila and shooting the s— with God. I will miss you forever, your advice, your laughter, your frankness. I will so miss you. I already do. I already feel it, this part of my heart missing. Deborah Waknin Harwin I love you.”

Sarah Michelle Gellar, who is friends with Doherty and was also close to Waknin-Harwin, also paid tribute to the late stylist on her Instagram. Sharing photos of the three of them together throughout the years, the Buffy the Vampire Slayer alum, 47, wrote to Doherty, “I’m at a loss for words. @theshando there are so many things about Deborah Waknin that I love.”

“She taught me so much about style and fashion, but more than that she taught me about true friendship when I was very young in hollywood,” Gellar wrote in her post.

Explaining that she “didn’t have a lot of friends” when she first moved to Los Angeles, the star said she’s “eternally grateful” to Doherty and Waknin-Harwin for being there “to guide me, keep me company, be a shoulder to lean on and teach me how to make the perfect margarita.”

“Deb has now left us, but I know that she is still here in our hearts,” she shared. “I’m not sure why this lesson right now when there is already so much pain and we are already so scared, but I will try to find it.

“Everyone pls let your loved ones know how much you love them today (even if it’s virtual) Craig and Liv- you are in my thoughts and my prayers.”

A rep for Waknin-Harwin did not immediately respond to PEOPLE’s request for comment.