Christina Aguilera Sings 'Happy Birthday' to Fiance -- Plus See Her Adorable 2-Year-Old Daughter!

They grow up so fast!

Christina Aguilera wished her fiance, Matthew Rutler, a happy 31st this week (his actual birthday is April 14), but in a new video shared to her guitarist guy's Instagram on Wednesday, it was the couple's 2-year-old daughter who looked to be getting a lot older!

WATCH: Christina Aguilera and Matthew Rutler Adorably Give Daughter Summer Rain a 'Kiss Attack'

In the sweet Instagram, Summer shyly helps Rutler blow out the candles, after Aguilera gives her man a nice birthday serenade.

The family of three is so adorable together, it almost hurts.

WATCH: Christina Aguilera Teases New Music on Instagram: 'Finishing Touches to My Heart'

In February, Summer's mom and dad couldn't help but give their daughter the most adorable kiss attack.

Watch the video below for more.