Selena Gomez
Selena Gomez (right) with her friend Francia Raisa, who donated the kidney she received. Instagram / Selena Gomez

In a heartfelt Instagram post, pop star Selena Gomez has revealed that she had a kidney transplant over the summer as a result of her lupus. Sharing pictures of herself in a hospital bed and of her scar, Gomez said she wanted to explain why she's been laying low over the past few months.

"I'm very aware some of my fans had noticed I was laying low for part of the summer and questioning why I wasn't promoting my new music, which I was extremely proud of," she wrote on Instagram. "So I found out I needed to get a kidney transplant due to my lupus and was recovering."

In the post she reveals that her new kidney was donated by her friend, The Secret Life of the American Teenager actress Francia Raisa, who is pictured alongside the Good For You singer.

"She gave me the ultimate gift and sacrifice by donating her kidney to me. I am incredibly blessed. I love you so much sis."

"It was what I needed to do for my overall health," the singer explained. "I honestly look forward to sharing with you, soon my journey through these past several months as I have always wanted to do with you.

"Until then I want to publicly thank my family and incredible team of doctors for everything they have done for me prior to and post-surgery."

Gomez has released three singles in 2017. It Ain't Me featuring Kygo was released in March, and was followed by Bad Liar and Fetish. The 25-year-old hasn't been out promoting the singles for now-obvious reasons, leaving her fans wondering why.

The pop star also shared a photo of the scar on her lower abdomen.

Gomez revealed in 2015 that she had been diagnosed with lupus, a primarily genetic autoimmune disease with varying symptoms, in which the body's immune system can attack healthy tissue. The condition mostly affects women.

"Lupus continues to be very misunderstood," Gomez wrote, "but progress is being made," before linking to the Lupus Research Alliance.