Answer:
Arrigo Boito
Step-by-step explanation:
This quote is often attributed to William Shakespeare's Romeo and Juliet; however, this quote never actually appears in the the play.
It is actually found in the Italian opera Falstaff (which happens to be based on Shakespeare's Merry Wives of Windsor).
The line translates from the following:
"Come ti vidi
M'innamorai
E tu sorridi
Perché lo sai."