Yes, warm-blooded lizards have been discovered. They aren't dinosaurs, and this is not a drill. More precisely, a recent discovery is that the tegu, a popular species of monitor, can provide itself with endothermic body heat. The only strange thing about this, other than the fact that until recently, everyone knew lizards were cold-blooded, is that the tegu only uses its heating system at certain times of the year. Despite comprehensive studies being performed about the issue, nobody currently knows how the tegu generates the heat. The current hypothesis is that the reptile secretes a hormone that causes some of its body parts to go into overdrive, which produces heat. However, this hypothesis has not yet been proved. Expect it to be proved, disproved, or replaced by other theories in future studies. Another theory surrounding not only this endothermic lizard but the rise of warm-blooded animals in general is that endothermy evolved gradually, as breeding modified metabolic systems. As a result, many animals may have gone through phases where they had partial endothermy, as the tegu has been discovered to undergo.
Irwin, Aisling. "First warm-blooded lizards switch on mystery heat source at will" https://www.newscientist.com/article/2074982-first-warm-blooded-lizards-switch-on-mystery-heat-source-at-will/
Science Advances, DOI: 10.1126/sciadv.1500951