Selena Gomez hopes that her sweetheart Justin Bieber has a wonderful birthday.

Justin turns 18 today and his girlfriend 19-year-old Selena is elated to be celebrating her beau's official entry into adulthood.

The singer-and-actress appreciates the joy Justin brings into her life and wishes him nothing but joy in the coming year.

"Happy birthday to my best friend in the whole world!!! Have a great birthday baby! (sic)" Selena posted on her Twitter account today along with an attachment of a photo of the two of them together.

Justin is equally excited about reaching this milestone.

"I'm great," Juston told Ryan Seacrest on his On Air radio programme Thursday morning. "I feel so much different. It's been crazy the amount of people who've been hitting me up and giving me birthday wishes."

Justin has received support on his big day from fans and well-wishers all over the world.

"I know they're so amazing; [my fans are] so incredible," Justin gushed.

The Baby singer was presented with a Fisker Karma sports car on the Ellen DeGeneres show for his birthday. The Finnish hybrid design featuring a solar panel roof and eco-friendly interior are extremely rare and cost between $102,000 and $116,000.

Justin would rather cruise in his new automobile than do anything impulsive on his first day as an adult. Getting a lip tattoo is not a priority for the star.

"No, no, no, no, [I won't get a lip tattoo]!" Justin exclaimed. "I think they wash out in like a year anyway. I don't know if I'd go through the pain of getting one on my lip. I don't really have much, I think I'm going to get another place in L.A. but other than that, that's pretty much it."