Katy Perry and Mayer ‘seem to be back together’

Katy Perry and her ex-boyfriend John Mayer may have reignited their passionate romance.

The musicians broke up for the second time in March after dating on-and-off since last summer.

Apparently John was one of the guests at Katy's Memorial Day barbecue held at her Hollywood Hills home on Monday.

The former flames' flirtatiousness was obvious to partygoers.

"They seem to be back together -- or back together-ish," an onlooker told Us Weekly magazine. "They were very flirty and having a really good time together. They have good chemistry.

Another insider noted "they were definitely friendly" at the bash.

In recent weeks Katy has been romantically linked to Los Angeles based entertainment agent Michael Kives.

Although it is rumoured Michael wants to pursue something serious with Katy, the star reportedly can't get over John.

"She is still calling John because she can't let go. And he still reaches out to her too because he loves to string his exes along," an insider told Star magazine recently.

Notorious lothario John was apparently worried about how fast his relationship with Katy was going. He had met her parents and there were even reports the couple were planning to get engaged.

Katy was previously married to British comedian Russell Brand, but they officially divorced in February 2012.

John has dated a string of famous beauties including Jessica Simpson, Taylor Swift and Jennifer Aniston.