Toscano – a former American Idol contestant – was celebrating her 26th birthday at Crustacean Beverly Hills when in walked Lopez.
"Pia was shaking when Jennifer walked in the door because she was so excited," an onlooker tells PEOPLE of the birthday girl. "She was so touched that Jennifer attended."
Toscano sang backup for Lopez when the Idol judge performed her hit single "I Luh Ya Papi" on the hit Fox reality singing competition last season.
"Jennifer was one of a handful of people that actually brought Pia a gift," says the onlooker. "And it was the biggest basket in the bunch!"
Lopez attended the party with her pal Leah Remini, and the two shared a cocktail (the Sweet P, named after the birthday girl) with Toscano and chatted the night away in a cabana.
Lopez and her gal pal left just before midnight, but not before snapping a selfie!
Ain't no good can come of this...lol it's LeTigre and Bunny and we like the boom...hahaha