ANSWER:

The scientist’s office faced east, and the sun was coming in through the window at a very low angle. He saw some very faint shadows on the surface of the envelope. He looked closer. There were the words embossed on the paper.

They read “Happy Birthday, Friend”. The ex-boyfriend had forgotten that a pencil leaves an impression on paper beneath the page written on.

I hope you had fun finding the answer to the riddle!! Don’t forget to share it with your friends!!