katy perry - russell brand - cartier INFphoto; bauergriffin

Katy Perry was spotted on the arm of fiance Russell Brand out and about in London this weekend sporting her beautiful Cartier engagement ring! According to the Diamond Information Center, the Cartier sparkler is an estimated 3-carat round diamond set atop a yellow gold band. The comedian proposed to the singer during a spiritual ceremony while vacationing in Thailand. Congratulations to the happy couple!