katy perry russell brand engagement ring

Katy Perry kissed Russell Brand and got diamonds! Photos: FilmMagic.com

Katy Perry braved the winter chill this weekend and showed off her engagement ring when returning to fiance Russell Brand's London flat in Hampstead after celebrating their engagement in Thailand.

She took to Twitter early Saturday and proclaimed to her fiance, "I love you @rustyrockets (awwwww...barf)." (Our thoughts exactly.)

Perry, 25 and Brand, 34, got engaged -- after dating for four months -- on New Year's Eve while on vacation in Jaipur, India.

The trip, "was his Christmas gift. She told him how much she loved Indian culture while they were eating curry in England, so he surprised her," a source told Us Weekly.

The eccentric comedian popped the question to the "I Kissed a Girl" singer in a spiritual ceremony with what the Diamond Information Center estimates is a 3-carat round-shaped center stone set on a vintage-esque yellow gold band from Cartier, with an estimated price tag of $120,000.

(We kinda thought fruit-loving Perry would opt for pear shaped.)

Cartier was reached, but declined to comment on its client's purchases.

Want the 411 on buying bling-bling on a budget? Click here for advice from diamond trend expert Francesca Ferrante of the Diamond Information Center.