Denise Richards Mourns 'Best Friend' and Ex Patrick Muldoon After His 'Heartbreaking' Death: 'You’ve Protected Me More Than Anyone'

Denise Richards broke her silence after ex Patrick Muldoon passed away suddenly at age 57 on Sunday, April 19.

On Tuesday, April 21, the actress uploaded a touching tribute to the late star and shared a montage of photos from their time together.

"This is so hard for me to put into words. I am deeply heartbroken & devastated losing you. You were my best friend & my family," the mom-of-three began her post.

Richards, 55, recalled meeting him in acting class when she was 19 while he was a 21-year-old USC student who nabbed a gig on Who's the Boss?.

"Here we are. 36 years later. My whole adult life & I don’t know it without you. The friendship, love, support, respect & loyalty we had was unconditional and rare," she gushed. "You lit up every room you walked into. You are larger than life & Everyone was drawn to you. So talented & most underrated actor. And most humble."

"Everything you did was infectious. Your laugh, your kindness, your wit, your strength, your loyalty, your passion, and your zest for life," Richards 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," Richards said. "Especially during this last year of pain & heartache. And now I need you more than ever, for this pain and heartache losing you."

The Melrose Place alum also revealed a nickname she had for her former costar, whom she dated from 1997 to around 2000.

"Schweetbabe we’ve had those conversations.. We thought we’d live forever or at least into our 90’s," she concluded. "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. 💔🙏🪽."

The realty star's daughter Lola Sheen, 20, honored the actor in her own social media post.

"I thought you were the one that was supposed to be in our lives forever. When I think of my childhood, I think of you, Pat," the actress' youngest daughter with ex-husband Charlie Sheen wrote. "It's gonna be so weird to go on without you in our lives. You were such a huge part of our family and life will never feel the same, but that's just because of how much you impacted us. Thank you for showing everyone around you how to be alive. You were the definition of what it means to have fun."

As OK! reported, Muldoon's passing was confirmed by his manager after he suffered a heart attack at his and his girlfriend's home in Beverly Hills, Calif.

Though she called the paramedics after finding him on the floor in the bathroom, he wasn't able to be revived.