Blake Shelton’s rumored romance with Gwen Stefani started is making rounds soon after he and Miranda Lambert announced their divorce in July. “The Voice” coaches have been spotted flirting on the show’s sets and were recently seen at a Halloween party in some PDA action. However, Shelton closeness to Stefani has “shocked” Lambert, according to Hollywood Life.

Lambert seemed surprised to see Shelton moving on quickly after their separation, and was jealous of Stefani, a source told the entertainment website.

“How could she [Lambert] not be just a tad bit jealous? Gwen is absolutely gorgeous and Blake appears to be completely smitten with her,” the insider told Hollywood Life.

“Miranda could tell by watching them on the show that they had a certain chemistry. … but she never knew it would develop into such a close relationship so fast,” the source added.

Shelton, 39, and Stefani, 46, were reported to be getting cozy with each other at Adam Levine and Maroon 5’s Halloween party in Studio City, California. The country singer was spotted moving his hands down to Stefani’s waist and at one point, even had a hand on her backside.