The world lost a true legend.

Hugh Hefner passed away on Wednesday from natural causes at age 91, and countless celebrities and former playmates took to social media to pay tribute to the Playboy founder. The media mogul's son Cooper announced his father's death on Twitter, and almost immediately the memories began to roll in.

"My father lived an exceptional and impactful life as a media and cultural pioneer and a leading voice behind some of the most significant social and cultural movements of our time in advocating free speech, civil rights and sexual freedom. He defined a lifestyle and ethos that lie at the heart of the Playboy brand, one of the most recognizable and enduring in history. He will be greatly missed by many, including his wife Crystal, my sister Christie and my brothers David and Marston, and all of us at Playboy Enterprises," Cooper wrote in the statement.

Here are some stars most touching reactions:
    Kim Kardashian: “RIP to the legendary Hugh Hefner! I’m so honored to have been a part of the Playboy team! You will be greatly missed! Love you Hef! Xoxo."
    Paris Hilton: "So sad to hear the news about Hugh Hefner. He was a #Legend, innovator & one of a kind. We had so many fun & incredible memories together. I will miss him dearly. Rest In Peace my friend.”
    Kendra Wilkinson: "Hef changed my life. He made me the person I am today. I couldn't be more thankful for our friendship and our time together. I will miss him so much but he will be in my heart forever."
    Bridget Marquardt: "So sad but forever grateful for all the wonderful memories and amazing experiences #RIPHef #Playboy 💔."
    Jenny McCarthy: "RIP #Hef Thank you for being a revolutionary and changing so many people's lives, especially mine. I hope I made you proud. 😓#PMOY 94 ❤️."
    Heidi Montag: "RIP @hughhefner 💛 thank you for making me part of the Playboy family. Sending lots of love and prayers to @crystalhefner."
    Jenna Dewan-Tatum: "Playing bunny Janie on The Playboy Club will always be such a positive memory for me. I made some of my dearest friends. Met Hugh while screening the pilot episode at the Playboy mansion with my dad and he couldn't have been more lovely. RIP🙏🏻."
    Aubrey O'Day: "@hughhefner ..when I did playboy he spoke words to me that affected my direction. he was a man the room would stop for when he entered #rip."
    Cindy Crawford: "Remembering an American icon and a true pop culture trailblazer. Honored to be part of the @Playboy legacy alongside my friend @HerbRitts. Rest In Peace #HughHefner ❤️."


The person most upset is Pamela Anderson, who was extremely close with Hefner and considered him family.

"Goodbye #Hef Mr Hefner I have so many thoughts, I have no brain n right now to edit I am me because of you You taught me everything important about freedom and respect. Outside of my family You were the most important person in my life. You gave me my life... People tell me all the time That I was your favorite... I'm in such deep shock. But you were old, your back hurt you so much. Last time I saw you You were using a walker. You didn't want me to see. You couldn't hear. You had a piece of paper in your pocket you showed me - with my name Pamela with a heart around it. Now, I'm falling apart. This feeling is so crazy. It's raining in Paris now. I'm by the window," she wrote.

"Everything anyone loves about me is because you understood me. Accepted me and encouraged me to be myself. Love like no one else. Live recklessly With unfiltered abandon. You said the magazine was about a girl like me. That I embody the spirit you fantasized about. I was the one. You said. I can hear you say - Be brave. There are no rules. Live your life I'm proud of you. There are no mistakes. And with men - Enjoy ... (Your wonderful laugh) You have the world by the tail You are a good girl And you are so loved - You are not crazy. You are wild and free Stay strong, Stay vulnerable. ... "It's movie time" You loved my boys ... You were always, always there for us. With your love Your crazy wisdom. I will miss your everything. Thank you for making the world a better place. A freeer and sexier place. You were a gentleman charming, elegant, chivalrous And so much fun. Goodbye Hef ... Your Pamela 💋," she added.

It's the end of an era!