Both her and Yunho participated in the musical Gwanghwamun Sonata, and this photo seems to be from then

https://instagram.com/p/zwQckNw_cK/

[Trans] 

organizing photos..when was this.. time passes so fast.. so nostalgic.. #gwanghwamunsonata #japan -rest of hashtags on names omitted-

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Credits:

Lisa Chung’s Instagram (nanlisada)
Translated by @snxy
Shared by TVXQ! Express