The 54-year-old, who once said "God, no, I couldn't have children", is over the moon since his first son Eric was born on Friday.
Simon has been sharing photos of his adorable new addition via Twitter, including this shot of himself, girlfriend Lauren Silverman and their new baby.
"Mum, Dad and Eric. Now two days old," he captioned the shot of himself snuggling their tiny son.
"Now you can see how very handsome little Eric is," Simon wrote with a close up shot of the newborn, who was named after Simon's dad.
The X Factor judge is smitten with Eric, saying: "I never knew how much love and pride I would feel," in another pic of him cradling his sleeping son.
We love seeing this softer side of Simon, and are happy that daddy duty seems to be his favorite job yet.