Lindsay Lohan and Tiffany Trump Party on Mykonos

How's this for a Grecian Formula ... Tiffany Trump and Lindsay Lohan in Mykonos.

Tiff and LiLo partied Friday night at a fundraiser to help victims of the Greek wildfires.

Turns out Donald Trump's youngest daughter and Lindsay are old buds and have actually hung out a lot over the years.

Lindsay opened a club called Beach House Mykonos earlier this year. As for Tiffany ... she's spending the summer overseas after finishing her second year at Georgetown Law School.