Demi Lovato is singing Selena Gomez's praises after the 25-year-old actress and singer revealed to the world she underwent a kidney transplant. "I think that she is a very strong woman," Demi told People on Friday evening after a performance in Los Angeles. "I'm very happy and proud of her," she gushed. Selena and Demi's friendship had been on and off for a few years, with Demi revealing in a 2014 interview that she and Selena had grown apart. The former Disney stars reunited in 2015 and shared an adorably silly selfie on Instagram confirming their friendship was back on the mend. "Friends for years, #sameoldlove," Demi captioned the photo.