WASHINGTON • Pop star Selena Gomez dropped a bombshell on Instagram: The 25-year-old had a kidney transplant this summer and the donor was a friend, actress Francia Raisa, 29.

The first photo in the post features Gomez and Raisa holding hands, lying side by side in hospital gowns.

"She gave me the ultimate gift and sacrifice by donating her kidney to me," Gomez said of Raisa, who is best known for the television series The Secret Life Of The American Teenager. "I am incredibly blessed. I love you so much sis."

The singer, who has the biggest following on Instagram with 126 million followers, revealed a large red scar across her abdomen in another photo in the series.

She said she needed a transplant as a result of having lupus, an autoimmune disease that can cause damage to many organs, including the kidneys, heart and brain.

She explained that she had been lying low this summer because "I found out I needed to get a kidney transplant due to my lupus and was recovering. It was what I needed to do for my overall health".

She felt the need to address her public absence after fans started wondering what happened to her, especially considering she had new singles to promote. When a pop star falls off the radar, the tabloid gossip inevitably gets going.

This is not the first time Gomez has disappeared due to health issues. In January 2014, she cancelled a number of concerts and the assumption was that she had checked into a rehabilitation facility for addiction.

The following year, she divulged that she had actually been undergoing chemotherapy after her lupus diagnosis.

Since then, she has been open about her struggles with the illness. Last year, she again cancelled part of her tour, saying she was suffering from anxiety and panic attacks caused by lupus.

She was well enough to release three singles this year. She also did press in spring for the buzzy Netflix series 13 Reasons Why, which she produced.

"I honestly look forward to sharing with you soon my journey through these past several months," she wrote of her ordeal on Instagram.

The cause of lupus is not clear and symptoms can include swollen joints, fatigue, rashes and fever.

"Lupus continues to be very misunderstood, but progress is being made," she said, directing her fans to the Lupus Research Alliance website for more information.

WASHINGTON POST, REUTERS