No it wasn’t,it was revealed *before* he was born…
“But while he thought on these things, behold, the angel of the LORD appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the HolySpirit 21 And she shall bring forth a son, and thou shalt call his name JESUS” (Matt 1:20-2)

“And knew her not till she had brought forth her firstborn son: and he called his name JESUS.”
Matt 1:25 (KJV)

And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
Luke 1:31 (KJV)