Cameron Diaz gave Drew Barrymore's partner her blessing to propose

Cameron Diaz knew about best friend Drew Barrymore's engagement before the bride-to-be herself because Will Kopelman sought the The Mask's star permission before proposing.

Art consultant Kopelman popped the question to Barrymore during a winter break in Sun Valley, Idaho, and the pair is rumoured to be exchanging vows on Saturday.

Diaz fully approves of her pal's partner and even gave Kopelman her blessing to make Barrymore his wife.

She tells InStyle magazine, "I knew Drew was getting married before she did."

Barrymore's previous two marriages to bar owner Jeremy Thomas in 1994 and comedian Tom Green in 2001 were short-lived - both lasted less than five months.