Jessica showed a lot of love for her younger sister Krystal. 

On Jessica's recent appearance on a Chinese talk show, she was asked about her idol star sister. Jessica commented, "My dongseng is much prettier. You can't beat young age. She is about 5 years and 6 months younger than me." 

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She continued, "Su Jung looks like my dad, and I look like my mom. We don't look very similar to begin with." Jessica then complimented Krystal, saying, "I think because we work in the same field we became more close and are able to relate better. She also often writes me letters. One time I was working while Su Jung was on a trip with our mom. She always sent me post cards and encouraged me with heartwarming words." 

The MCs also asked if she gives Krystal dating tips, and Jessica answered, "Of course."