The birth that the world has been anticipating has arrived with the arrival of Prince William and Kate Middleton's first baby boy. The news broke just after 3:30 ET and social media lit up with immediate fervor.

The hashtags #Royalbaby, #royalbabyboy, #royalcongrats, and #itsaboy are rapidly climbing the trending tags on the twittersphere.

The new addition to the royal family came in at a healthy 8lbs, 6oz at 4:24 London time.

Celebrities all over are reacting to the birth. Stars Olivia Wilde, Ellen Degeneres, Snooki, and Piers Morgan just a few of the celebrities to react to the birth.

Even Severus Snape (@_Snape_) had one to offer: Dear William & Kate: If William is 100% royal and Princess Kate is 0% royal, will that make your son a half-blood prince?

The British Monarchy even took to twitter to announce the birth, tweeting a picture of the birth announcement.

The baby shares his birthday with the likes of Selena Gomez, Rhys Ifans, and Alex Trebek.

There has not yet been an announcement on the name of the baby, though it is expected to come soon. Names such as James, George, William, and Philip stand among the top of predictions.