Khloe shared a photo on Snapchat from her workout with Tristan before they returned home and tested out a giant water slide for the bash. She followed up with a video of herself and Kris at the party.
"Happy Fourth of July!" the pair wish their fans.
Rob attended the fete with Dream, his 7-month-old daughter with ex-fiancee Blac Chyna. He posted a series of pictures with Dream on Instagram, including a snapshot of himself holding his baby girl in Khloe's pool.
"Happy 4th! Everyone be safe !!! Love," the 30-year-old reality star captioned the photo.
Khloe and Tristan, who plays basketball for the Cleveland Cavaliers, were first linked in October.
Tristan helped surprise Khloe with a party ahead of her 33rd birthday in June, and dedicated a sweet message to the star on her actual birthday.
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"Happy bday my love," he wrote June 27. "Let's continue to build more memories and cherish them with each other. God bless you, I love you."
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