Former lovers John Mayer and Katy Perry reunited on America's Memorial Day (27May13) when the I Kissed A Girl singer opened her Hollywood Hills home to friends for a summer party. The couple, which split for the second time earlier this year (13), was spotted chatting and flirting with each other at the bash. A source tells Us Weekly magazine, "They seem to be back together-ish. They were very flirty and having a really good time together. They have good chemistry." Other party-goers included Mindy Kaling, BJ Novak and Beth Behrs, as well as Perry's actress pal Allison Williams and her boyfriend Ricky Van Veen, who is one of Mayer's closest friends.