Kate Hudson, Avril Lavigne Sing Duet at David Foster's Star-Packed Wedding

Why'd they have to go and make things so complicated?

Canadian songwriter/producer David Foster said "I do" to model Yolanda Hadid on Friday, Us Weekly confirms. But the bride and groom weren't the only stars of the day: a source tells Us that Avril Lavigne and Kate Hudson sang a duet. (Hudson, 32, sang in Rob Marshall's 2009 musical Nine.)

PHOTOS: Kate Hudson's bikini body

Lavigne, 27, attended the ceremony with boyfriend Brody Jenner; Foster, 62, was married to Jenner's mom Linda Thompson from 1991 to 2005.

PHOTOS: Hot Canadians

Fellow Canadian Michael Buble crooned at the reception, and Kenny G went from table to table playing his saxophone at dinner.

PHOTOS: Over-the-top celebrity weddings

The groom's daughter, Erin, was in attendance with pal Samantha Ronson. Lindsay Lohan's ex "tried to DJ, but was told no," said a source.

This was the fourth marriage for Foster, who is known for composing tracks like "Grown Up Christmas List" and "I Have Nothing," as well as discovering artists including Buble, Josh Groban and Charice.

Get more Us! Follow us on Twitter, Friend us on Facebook, Subscribe to Us Weekly