The boys shared on twitter the photo you see above as they wrote, "With Taeyeon sunbaenim who played a big role in helping us decide on the name of our title track!! We saw her at 'Music Bank' ehhaha", and made fans jealous with a group shot with the ballad princess.
BTS looked 'in luv' upon meeting the beautiful Taeyeon and they expressed their happiness with V-signs.
If you're wondering what this is all referring to, the boys previously revealed that they heard Taeyeon's comment that she likes the manly-man style upon watching BTS' stage at the '28th Golden Disk Awards'. So the boys decided to name their song "Manly Man" in Korean (but they use 'Boy in Luv' as the international title for fans overseas).