(CNN) -- Paul Walker's sudden death has left many in Hollywood nearly too stunned to speak.
As the news of his death spread on Saturday, some celebrities, including Lady Gaga and Alyssa Milano, tweeted their disbelief.
Adored for his work in the "Fast & Furious" movie franchise, Walker was in the midst of filming a seventh installment at the time of his death. Two of his co-stars in the blockbuster series, Ludacris and Tyrese, expressed their grief on social media.
"I can't believe I'm writing this," singer/actor Tyrese shared on Instagram, along with a photo of himself with the late star. "My heart is hurting so bad no one can make me believe this is real Father God I pray that you send clarity over this cause I just don't understand ... My heart hurts it's broken no one can convince me that this is real.... Prayer warriors please pray real hard for his only child, his daughter and family..."
Ludacris, meanwhile, remembered Walker for his "humble spirit" with a verse: "Wherever you blessed your presence you always left a mark, we were like brothers & our birthdays are only 1 day apart, now You will forever hold a place in all of our hearts."
The 40-year-old actor, who rose to fame in 2001's "The Fast & The Furious" after appearing in '90s hits "She's All That" and "Varsity Blues," died in a car accident. He'd been attending a charity event for his organization, Reach Out Worldwide.
Throughout the industry, several are mourning the loss of a great friend and, by their account, giving humanitarian:
Paul was a good dude. Conscientious & not caught up in Hollywood. He knew there was more to life & lived like it. Nice to know you brotha.— Ryan Phillippe (@RyanPhillippe) December 1, 2013
Thoughts and prayers tonight are with Paul Walker's friends and family, especially his little girl. So sad. Very heavy heart tonight.— James Van Der Beek (@vanderjames) December 1, 2013
My heart is crushed by the news that my friend Paul Walker passed away today. Prayers and light to his daughter and family right now.— Michael Ealy (@MichaelEaly) December 1, 2013
Sad and shocked to hear about Paul Walker. Knew him. Liked him. Rest in peace.— scott foley (@scottkfoley) December 1, 2013
Paul was a truly good person in a town of questionable characters. ..A real life tragedy if there ever was one.— Rachael Leigh Cook (@RachaelLCook) December 1, 2013
Heavy heavy heart tonight. Paul Walker was a genuinely good, sweet, kind, laid back, loving person. Sending much love to his family.— olivia wilde (@oliviawilde) December 1, 2013
I'm a devastated right now. My prayers & condolences go out to Paul Walkers family & friends. He was a amazing talent & will truly b missed— Kevin Hart (@KevinHart4real) December 1, 2013
Tellingly, Walker's passing was felt throughout the entertainment world, as even those outside of acting took a moment to reflect on the sobering death.
I didn't know him well at all, but I know that the world lost an incredibly kind man in Paul Walker today. So truly sad.— Zachary Levi (@ZacharyLevi) December 1, 2013
Oh man just read about Paul Walkers death. So young. Ugggh makes me sick especially when it's caused by an accident. God bless his soul.— Jay Sean (@jaysean) December 1, 2013
Walker's next film, "Hours," is scheduled to be released on December 13.