Lee Joon was caught off guard after the cast of "Running Man" mentioned their experience dating fellow celebrities.

"The Escape of the Seven" star recently guested in the latest episode of the SBS' show, where the host unexpectedly brought up the past relationships of everyone.

Lee Joon Was Taken Aback by the Challenege in 'Running Man'

As obtained by a news portal, part of the challenge was to get on the van to transfer to the next location; however, only six of them will be accommodated, which means that the rest who were unable to get inside the vehicle should commute via public transportation.

To narrow the options, Ji Suk Jin recommends that only people in a relationship should onboard the van.

"Raise your hand if you have a boyfriend, girlfriend, husband, or wife. You are the ones who should get in the car," he said.

Joining Suk Jin, who is married, Jeon So Min also raised her hand, claiming that she and Yang Se Chan are qualified, referring to their fake on-screen relationship.

Meanwhile, HaHa made it more exciting and said that only people who date celebrities should get inside the van.

In this case, Jeon So Min, who once mentioned that she used to date a member of a K-pop boy group, raised her hand.

As for the "Running Man" guest, Lee Joon initially hesitated to raise his hand and was concerned that his past relationship would be brought up, but eventually caved in and raised his hand.

"This is driving me crazy!" he said, hinting about his celebrity ex-girlfriend; however, Lee Joon didn't drop the name of the person, but despite it, the cast and viewers knew to whom he was referring.

Lee Joon Dated Jung So Min After Starring in 'My Father Is Strange'

In 2017, Lee Joon headlined the rom-com K-drama "My Father Is Strange," along with veteran actress Kim Hae Sook, Jung So Min, and more.

Interestingly, other than being co-stars, the duo have a lot of similarities. They both lived in the same neighborhood and went to school in Bundang.

In 2018, they went public and admitted their relationship. At the time, they'd mentioned through their respective agencies that they started dating after "My Father Is Strange," where they played as a couple.

Unfortunately, news broke that Lee Joon and Jung So Min had ended their nearly three-year relationship.

As for Dispatch's source, the duo have "decided to remain on good terms and cheer each other on as fellow actors."

Other sources also mentioned that their busy schedules and spending a lot of time apart were the reasons behind their breakup.

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Written by Geca Wills