Selena Gomez became a big sister last week when her mother delivered a healthy baby girl.

And when Justin Bieber heard the baby was born, he couldn’t’ wait to reach on to his ex to offer his congratulations.

Even though Selena Gomez’s mom Mandy Cornett  is not the biggest fan of the Biebs, he is still trying to stay in the good graces of his on-again, off-again girlfriend of two years.

 “Justin knows the joy of younger siblings and is very happy for Selena and her Mom. He wished Selena the best and is working on getting a gift,” a source told Hollywood Life.

After a report surfaced saying Gomez’s 37-year-old mother had given birth to a daughter, Gomez took to Twitter to give her fans all the details.

“Momma, Brian, and me are all so grateful for all your well wishes. My lil sissy Gracie Elliot Teefey was born on June 12th.,” wrote Gomez.

Days before the baby was born, Gomez said in an interview she was planning on spoiling her little sister rotten.

"I want to be the best sister in the world. I'm really going to spoil the babyhttp://images.intellitxt.com/ast/adTypes/icon1.png!” she told aufeminin.com.

''There's going to be a big age difference, so I think I'm going to be more like a cool aunt.”

Just last month on Mother’s Day, the 20-year-old triple threat shared a picturehttp://global.fncstatic.com/static/v/all/img/external-link.png revealing her mother’s pregnancy.

"Hope all the amazing moms had a great day!” Gomez tweeted along with a picture of her holding her mom’s expanding belly. “I have the best momma in the world :)) I love you so much!"

The birth of her sister Gracie comes as a happy note for the family as her mom suffered a miscarriage in December 2011.

Gomez’s mom divorced Selena's father, Ricardo Gomez, when the singer was 5-years-old and remarried her current husband, Brian Teefey, in 2006.

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