The Bad Liar singer had previously kept quiet about the procedure, keeping herself out of the limelight and only sharing the news on Instagram last month.
And she has now opened up about the severity of the operation, revealing it was “life or death”.
In an interview on the Today show, the 25 year old explained: “I guess I got to the point where it was really kind of life or death. My kidneys were just done.”
But, although she was suffering with the diagnosis, she was adamant she didn’t want to ask “a single person in [her] life” for help – before pal Francia Raisa came forward.
“That was it and I didn’t want to ask a single person in my life,” she continued. “And she volunteered and did it.”
The brunette beauty has credited her 29-year-old pal for saving her life – and admitted she “rescued” her.
Selena Gomez shows off her new short haircut [Justin Tranter/ Instagram]
The NHS define Lupus as a complex and poorly understood condition that affects many parts of the body – with symptoms ranging from mild to life-threatening.
It is an autoimmune condition, which means it’s caused by problems with the immune system.
For reasons not yet understood, the immune system in sufferers starts to attack and inflame healthy cells, tissue and organs.
Selena recently made headlines after speaking out about the transplant, following months of secrecy.
Taking to Instagram, the Spring Breakers star shared a snap of herself in a hospital bed, next to her best friend – as well as a photo of her scars – she opened up about her battle.
“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 told her 128million followers.
“So 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. 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.
“And finally, there aren’t words to describe how I can possibly thank my beautiful friend Francia Raisa. She gave me the ultimate gift and sacrifice by donating her kidney to me.
“I am incredibly blessed. I love you so much sis. Lupus continues to be very misunderstood but progress is being made.”