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Seo Kang Jun and Lee Kuk Ju came up with the idea to prank Jackson upon arriving at his showcase, and Seo Kang Jun went up to meet Jackson backstage first while Lee Kuk Ju waited to surprise him as his 'mother'. He then asked Jackson, "Now that you're doing a showcase, doesn't your mother come to mind?", to which Jackson replied, "I'm always thinking about her." Seo Kang Jun asked, "You miss your mom, right?", and Jackson said, "Yes." Seo Kang Jung then implied to Jackson that his mother is really here and told him to call out to his mother over and over, which led the surprised Jackson to start tearing up at the thought of his mom being there. 

However, once Lee Kuk Ju walked though the door, the look of disappointment on Jackson's face was hard to ignore. Jackson later shared in his interview, "To be honest, I really thought that my mom came. I thought, 'Is my mom really pulling a surprise for me? Did she really come to Korea?' I honestly almost cried."

But to make up for the prank, Lee Kuk Ju asked that Jackson be given an opportunity to call his mom on her phone, leading to a heartwarming moment for everyone there and those watching.

Starts at the 24:20 mark.