Khloe Kardashian Accidentally Turns Up at Same Las Vegas Concert as Ex James Harden

A source tells ET that 'tension was tight' at Drai's Nightclub on Friday.

Khloe Kardashian was one busy girl in Las Vegas!

Not only did she steal the show at Scott Disick's second birthday party at 1OAK inside The Mirage Hotel & Casino on Friday, she managed to find time to attend Future's sold-out performance at Drai's Nightclub that same night.

WATCH: Khloe Kardashian Stuns in Skintight Latex Dress at Scott Disick's Vegas Birthday Party

The problem? Kardashian's ex-boyfriend, James Harden, was also at the concert.

A source tells ET that both of them being there was "coincidental" rather than a planned run-in.

"The tension was tight, and they were making eyes at each other," the source said, noting that Kardashian went straight to the airport after the show.

WATCH: Khloe Kardashian and James Harden Call It Quits

The 31-year-old reality star shared a few photos on Instagram from her fast-paced night, including one of her and BFF Malika Haqq giggling. Haqq and Kourtney Kardashian were also in Sin City to help Disick ring in his 33rd birthday.

"We definitely were talking s**t! Lol that's my best friend," the Keeping Up With the Kardashians star captioned the post, which could hint at having seen Harden that night.

On Sunday, the queen of cryptic quotes shared another one of her infamous messages to Instagram, but since she's asked people to not read into her meme-esque posts before, we'll let you interpret this one:

WATCH: Khloe Kardashian Posts Star-Packed Pic of Jennifer Lopez's Girl Squad

Kardashian and Harden split in February after having first stepped out together in July 2015.

The outspoken reality star got candid about the breakup on her now-cancelled talk show, Kocktails With Khloe, claiming that the Houston Rockets guard wasn't monogamous during their time together.

She alleged that she had offered up the option of a non-monogamous relationship since they were long-distance but that Harden insisted on being exclusive.

"He wanted [a relationship]," Kardashian says. "I wanted it, but I wanted to be realistic. He sought me out. He wanted to be committed and, you know, then wasn't committed. So Koko had to go go!"

WATCH: Khloe Kardashian Reveals the Bizarre Way She Got Her First Thong at Age 13

The pair were dating when Kardashian's estranged husband, Lamar Odom, entered the hospital in October after being found unresponsive at the Love Ranch Brothel in Crystal Ranch, Nevada. Kardashian supported the former NBA pro throughout his recovery but has since filed for divorce from him for a second time.

The couple married in 2009 after one month of dating. The reality star first filed for divorce in December 2013, but she put the proceedings on hold shortly after Odom’s health scare.

WATCH: Khloe Kardashian Files For Divorce From Lamar Odom For the Second Time