Selena Gomez (R) hugs her mother Mandy Cornett
Selena Gomez (R) hugs her mother Mandy Cornett Reuters

American singer Selena Gomez took to Twitter to welcome her new baby sister. The 20-year-old Disney star's mother, Mandy Cornett, and step-father Brian Teefey, celebrated the birth of their first child together, earlier this week.

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

The Wizards of Waverley Place star confirmed her mother's pregnancy on Mother's Day, tweeting a photograph of the two of them together, with her stroking Cornett's blossoming baby bump.

Selena Gomez's mother, who is 37 years old, divorced the singer's father, Ricardo Gomez, when the couple's daughter was only five years old. Mandy Cornett married Teefey in 2006. The couple were expecting in 2011 but Cornett suffered a miscarriage.

Meanwhile, fellow American singer Demi Lovato was one of the first to celebrate the news, tweeting: "@selenagomez IS A BIG SISTER!!!!!! Everyone congratulate her and her family!!!!!! #CONGRATSSELENA!!!!"

It was previously reported Selena Gomez had reconciled with pop star boyfriend Justin Bieber. The two were believed to have agreed on a "trial period" to see if a relationship was possible. The 19-year-old Baby singer reportedly also sent his congratulations to the new mother.

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

Selena Gomez and Mandy Cornett Share Very Strong Bond

Prior to her rise to fame, Selena Gomez says she had a tough childhood and her mother went through a difficult period as a working single parent.

"I remember my mom would run out of gas all of the time and we'd sit there and have to go through the car and get quarters and help her get gas," Selena said in 2011, "Because she never liked to ask my grandparents for money."

"I remember having a lot of macaroni and cheese but my mom never made it seem like it was a big deal. She was really strong around me. Having me at 16 had to have been a big responsibility. My mom gave up everything for me, had three jobs, supported me sacrificed her life for me," she added.