AceShowbiz -

John Mayer and Katy Perry spark reconciliation rumor. The former couple, who split for a second time last March, is reported reuniting on Memorial Day at a barbeque party she threw for her friends at her Beverly Hills home.

"They seem to be back together -- or back together-ish," an eyewitness tells Us Weekly. "They were very flirty and having a really good time together. They have good chemistry." Another source adds, "They were definitely friendly."

They were joined at the gathering by Allison Williams and her beau Ricky Van Veen, who double dated with Perry and Mayer at the Grammys this year. Mindy Kaling, B.J. Novak, Beth Behrs, Shannon Woodward, Kate Micucci and Riki Lindhome were among the guests as well.

Katy never publicly confirmed that she's dating Mayer, but they were repeatedly seen going out together last June. They allegedly broke up in August before reconciling in September. "For the first time in my life I don't feel like I'm in a celebrity relationship. I know it is high profile. It's hard to explain... For me it feels like something that's very human," he once said.

In an interview with Ellen DeGeneres later after they broke up for a second time early this year, Mayer refused to spill the deets, "It was a very private relationship going in. It was a private relationship during, and it's a private relationship, still." He added, "Coupling is a tricky thing."