It all began when Donnie saw the door decorations of two huge NKOTB fans
, and stopped in to their cabin to say hello.
"If Donnie Wahlberg knocks on your door and tells you that you did a great job, than you must have done something right," said one of the two fans, overjoyed that the singer picked their room to visit.
Inside their cabin, the two girls had turned the room into a NKOTB shrine, complete with a life-size cardboard cutout that they had stolen from another part of the boat.
Instead of telling them to give it back, Donnie had a better idea: He revealed that another cardboard cutout existed on the ship, and he challenged the girls to find it, steal it, and get it back to their rooms without getting caught.
The season finale of Rock This Boat airs Wednesday at 8/7c on Pop TV.