The pair met while filming 1997’s Starship Troopers and dated for nearly five years, remaining close friends afterward

Denise Richards paid tribute to her close friend and confidant, actor Patrick Muldoon, who died at the age of 57 on Sunday, April 19, following a heart attack. The pair met on the set of the cult classic Starship Troopers in 1997, and dated for nearly five years. Following their breakup, Richards and Muldoon remained close friends and supported each other throughout their careers.

“This is so hard for me to put into words,” Richards wrote in an Instagram post on Tuesday following news of his death. “I am deeply heartbroken & devastated losing you. You were my best friend & my family. We met in our first acting class, I was 19 never had an acting job and you were 21 a student at USC doing a recurring role on who’s the boss. And here we are. 36 years later. My whole adult life & I don’t know it without you.”

Richards shared the heartfelt tribute alongside a video montage of her and Muldoon throughout the years, from their time dating in the Nineties to clips of them later in life, setting the post to Bread’s track “Everything I Own.” The actress said the “friendship, love, support, respect & loyalty” they had was “unconditional and rare.”

She remembered how Muldoon “lit up every room you walked into” and how he was “larger than life,” calling him “most underrated actor.” She continued, “We’ve been each other’s rock. Our memories together are endless. You’ve had my back and protected me more than anyone. I don’t know what I’m going to do without you here. You’re my voice of reason & pillar of strength. Especially during this last year of pain & heartache.”

Before ending her message, Richards referred to him by the nickname they gave each other on the set of Starship Troopers and said, “And now I need you more than ever, for this pain and heartache losing you. Schweetbabe we’ve had those conversations.. We thought we’d live forever or at least into our 90’s. Schweetbabe I will be looking for those signs. I need to know you’re still here with me. I love you so much & miss you dearly schweetbabe.”

Muldoon was also known for starring in the popular soap opera Days of Our Lives as  Austin Reed, a role he embodied from 1992 to 1995, and again from September 2011 to July 2012. He also featured as the recurring character Richard Hart on Melrose Place for three seasons in the mid-Nineties. Muldoon’s latest film, crime thriller Dirty Hands, which co-stars Richards and Michael Beach, is slated to be released on April 24

“I tend to look at things backwards,” he said in 2012 when discussing what he gained from his experiences acting. “When you get a part there is something going on within that character. There is a question that the character is living at that time. There is probably something you need to look at from your own personal life. As things come to you I kind of look at it on a spiritual tip a little bit. Whatever obstacle that character has to face somehow I am being asked to look at that in my own life. In order to be able to play the part you have to look at it from your own life. That is generally what I pay attention to when a part comes across the desk.”