f(x)'s Sulli's school uniform photo has become a hot topic among netizens lately.

On April 1st, Super Junior's Heechul pulled off an April Fools' Day prank by switching his profile picture to Sulli and caption that read, "This is f(x)'s Sulli. The real Sulli."

Heechul later impersonated Sulli again, this time by uploading a photo of Sulli and tweeting, "The outfit in this photo is probably our school's uniform. Can't remember that well since it's been a while since I graduated Hehe."

A few hours later, he wrote another post that read, "I think I'm pretty, but I don't get why other people think so too. Aren't people like singers the ones that are pretty? There are plenty of girls at my church that are prettier than me, but why do people think I'm the cute and pretty one? I really dislike people that do that. When I tell them my name, they even think my name is pretty... Am I really that pretty?"�Heechul was actually quoting Sulli's old diary entry which was first revealed on the music talk show, 'Kim Jung Eun's Chocolate'.

Netizens commented, "The two must be very close", "Sulli is indeed very pretty", and "She looks like a doll even in school uniform."

Source: Heechul's Twitter