The 33-year-old singer stopped by the 36-year-old actress' game night Saturday, and the celebrity pair made sure to document the fun on Instagram.
"That moment when @britneyspears shows up to your game night and your all like #itsbritneybitch," Hudson captioned a photo of herself with the pop star.
"Two blondes... Too much fun. Loved hanging with you last night @katehudson!" Spears added.
The singer and the actress appear as close as sisters in the playful snapshots. The stars both have two sons: Spears is mother to 10-year-old Sean and 9-year-old Jayden, while Hudson is mom to 11-year-old Ryder and 4-year-old Bingham.
Spears released Britney Jean in December 2013, and recently extended her Las Vegas residency at Planet Hollywood into 2017. Hudson will next appear in Rock the Kasbah with Bill Murray, and is scheduled for Mother's Day with Jennifer Aniston and Deepwater Horizon with Mark Wahlberg.