"With absolute most certainty," the 27-year-old captioned photos of the moment Buss popped the question. The proposal took place outside a house and the pics showed Buss kneeling down to ask for Tallulah's hand before the couple shared a kiss.
"HANDS STILL SHAKIN’ — MOMS SPAGHETTI — I’m FIANCÉNCHED," Tallulah captioned a shot of her engagement ring.
Fans, friends and her famous family rushed to the comments to congratulate the bride-to-be.
"💍😭💍😭💍💍 weeping, i am so f*****g excited," sister Scout Willis gushed.
Scout also posted photos with her sister on her own account to celebrate. "I’m so buoyed by this JOYOUS LOVE CELEBRATION!!!! HIP HIP HURRAY!!!!! @buuski @dillonbuss today is a blessing because of your love! 5/4/21 💍 Welcome the first official WILLIS BROTHER 😭😭😭" she captioned the post.
"OMGGGGGGGGGG 😭😭😭😭," Stephanie Shepherd commented.
"So happy for you ❤️❤️❤️," Ireland Baldwin wrote.
"I love these crazy kids. Congratulations @dillonbuss and @buuski I love you both so immensely and I am so excited for you. 💍💍 💍💍💍 💍💍," Rumer Willis captioned a series of pictures of the couple.
Buss shared some of the couple's sweetest moments on his Instagram to mark the occasion. "I can finally call you my fiancée. Love you forever Buuski Lu, you are my best friend ❤️ #maythefourthbewithus," he captioned photos of the pair after she said yes.
It is unclear when Tallulah and Buss got together but he first appeared on her Instagram in February 2020. Prior to this the actress was linked to Jack Kilmer.
Buss is familiar with his future in-laws as both of Tallulah's sisters and their partners quarantined with their parents in Idaho amid the pandemic, Us Weekly reported.
"It’s been really funny having both my parents at this house where they, like, raised us," Scout said of the living situation on the "Dopey" podcast in April. "It’s kind of divine time to just hang out with them. … I’m very grateful to be with my family."