While many soaked up the sun, Christina Aguilera celebrated the first day of summer (June 21) by showing off her growing belly on Twitter!

The singer tweeted a photo of herself in a clingy purple dress that hugged her baby bump, along with the caption, "Happy 1st day of summer! Keep those lips hydrated!" In the pic, Christina is holding a tube of EOS lip balm.

It's been an exciting year for 'The Voice' coach, who announced her engagement to film producer Matt Rutler on Valentine's Day. (Awwww!) In March, Christina confirmed she's pregnant with a baby girl. Fingers crossed the baby inherits her mother's incredible voice.

The singer looked fantastic when she performed at Wango Tango in May, wearing a skintight black dress that showed off her growing baby bump. “I’m really excited to meet our baby girl,” Christina told PEOPLE. “This has been a very easy and enjoyable pregnancy.”

This will be Christina's second child and her first with her fiance. The singer has a son, six-year-old Max, from her previous marriage to Jordan Bratman.

See Christina Aguilera + More Pop Stars Without Makeup