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James Harden, Birthday Party, Khloe Kardashian

FAMEFLYNET/AKM-GSI

It's official: Khloe Kardashian and James Harden are one of the hottest couples of the summer.

The duo were spotted at the NBA player's celebrity-filled 26th birthday bash on Tuesday night, looking sexy in white-on-white ensembles that matched the party's yacht theme.

Khloé showed off some serious skin and her super-toned legs in a see-through skirt with two thigh-high slits, which she paired over a lacy white leotard that revealed just a hint of booty. However, she swapped out her swanky Christian Louboutin pumps for a pair of more comfortable white tennis shoes as she made her way off the boat at the end of the long night.

James Harden Birthday Party, Khloe Kardashian, Kim Kardashian, Kylie Jenner, Kris Jenner, Tyga, Kourtney Kardashian, Kanye, Kendall

FAMEFLYNET/AKM-GSI

Harden looked like he had the time of his life, still carrying a half-empty bottle and a couple gift bags as he followed his girlfriend off the yacht. He wore an oversize white shirt with white jeans and a pair of high-top sneakers.

Khloé wasn't the only member of the Kardashian clan in attendance. The Houston Rockets player's soiree included a long list of the reality star's family, including: Kim Kardashian, Kanye West, Kylie Jenner, Tyga, Kendall Jenner and Kourtney Kardashian. Even mom Kris Jenner and boyfriend Corey Gamble made an appearance.

The boat took off around 11 p.m. from Marina del Rey, Calif., and set off an impressive fireworks show at midnight. It returned at 1 a.m. to drop off the Kardashians and Jenners, with the exception of Khloé who stayed to party with her beau as more attendees hopped onboard to join the festivities. Everyone continued to dance, take photos in the photo booth and celebrate until about 3 a.m.

At one point in the evening, Khloé and Harden were spotted getting super cozy, affectionately hugging and whispering into each other's ear.

The cute couple was first linked together on July 4 after being spotted in Las Vegas together. A few days later, an insider told E! News the two are "hanging out and having fun."

Earlier this month, the duo headed to Houston where they were spotted on a very romantic date…at Chipotle (LOL!).  The two were said to be spending time in H-town to celebrate Harden's birthday ahead of his big bash this week.