Taylor Swift and nemesis Katy Perry attend Drake's 30th birthday party...along with their ex John Mayer

Now this is definitely a birthday party to remember.

Katy Perry, Taylor Swift, and John Mayer were all on hand at Delilah Los Angeles to help Drake ring in his 30th birthday, and given their history, the three of them together in one room probably caused a few double takes.

If you'll recall, Katy, 31, and Taylor, 26, have had a long-standing feud, which reportedly started after the 'Firework' crooner snagged some of Taylor's back-up dancers for her own performances.  Since then, both have made backhanded comments about each other on social media and in interviews.

They also both have dated John. The 'Gravity' crooner, 39, and Katy were off and on for years, last calling it quits in 2015 before she moved on to Orlando Bloom.

Taylor's relationship with John in 2009 was far more brief, but, it was still significant enough for her to write a song about it (in typical Taylor fashion). After they split, she headed to the recording studio and recorded 'Dear John'.

In spite of the beefs they've all had in the past (and present in the case of Katy and Taylor), Us Weekly reported that there was "no drama" at the party, and that John and Katy even talked to each other for a short time.

"Everyone had a great time and got along. No drama," a source told the site.

Meanwhile, an insider told E! News that Taylor and John didn't cross paths, and there have been no reports of Katy and Taylor chatting it up either.

Taylor has sure been dipping into the ex files lately. Just last weekend, she sang her Calvin Harris lyrical collaboration 'This Is What You Came For' in her first concert of 2016. Watch that video below.