Update: The fans have spoken -- and Britney Spears' 'Baby One More Time' is the Greatest Pop Song of the Modern era! Get more details here.

The final round of March Music Madness is here! Over the past several weeks -- and over the past four rounds -- you have voted for the Greatest Pop Song of the Modern Era, narrowing down 32 of the best pop songs from the '80s to today to the final two hits that will go head-to-head in the ultimate round. Only one song can be crowned the Greatest Pop Song of the Modern Era -- which will it be?

Last round, Britney Spears' 'Baby One More Time' was up against Michael Jackson's 'Billie Jean,' and it was an intense battle up until the last second! Ultimately, '90s-era Britney triumphed over the King of Pop, and 'Baby One More Time' garnered just more than 51% of votes. Talk about a close race! Lady Gaga's 'Bad Romance' also duked it out with Adele's 'Someone Like You,' and it won by a landslide with more than 63% of votes. Now, in the final round of March Madness, it's a battle of the pop divas, with Britney Spears' 'Baby One More Time' going up against Lady Gaga's 'Bad Romance.' Which tune is most deserving of the title of Greatest Pop Song of the Modern Era?

You know Britney Spears' 'Baby One More Time' has staying power when it beats out 'Billie Jean,' one of the King of Pop's biggest hits! Though Spears has since become a legendary pop icon since she first burst onto the scene with 'Baby One More Time,' the song is arguably still her most famous to date. In the '90s, it topped the charts and earned Ms. Spears a Grammy nomination -- and today, it routinely makes countless 'Best of' lists and has become one of the best-selling singles of all-time. When you think Britney Spears -- heck, when you think pop music -- 'Baby One More Time' is undoubtedly one of the first in your mind. It's a classic.

Can Lady Gaga hold her own against Britney Spears? 'Bad Romance' was a mega hit for the singer, winning her two Grammy Awards and ultimately going a whopping 10x platinum. 'Bad Romance' is classic Gaga, showing off her powerful voice and proving that she has the vocal chops and individuality to go up against Spears -- and make our final round of voting a tough competition between the Britney Army and Little Monsters.

Which song should be crowned the Greatest Pop Song of the Modern Era? You can vote for 'Baby One More Time' or 'Bad Romance' once every hour until the polls close at 12PM ET on April 8. The ultimate victor will be announced on the same day, and, finally, we will have crowned one hit the Best Pop Song of the Modern Era.

Be sure to check out the contest at the bottom of this page to enter to win a $100 iTunes gift card after you’ve voted. It’s a gift from us to one of our lucky readers for taking part in March Music Madness!