'The Big Bang Theory' star Kaley Cuoco is engaged

'The Big Bang Theory' star Kaley Cuoco is engaged to boyfriend Karl Cook.

After two years of dating, Cook popped the question to the 32-year-old on her birthday and shared the special moment on his Instagram account.

"Well after nearly two years I finally got up the courage to ask her to marry me. This is the best night of my life and I think the video shows it is the best night for Kaley as well...." he wrote in the caption.

"We're engaged!" the actress says in the video.

"Still crying every part of this night has been perfection just like you @mrtankcook I love you forever!" Cuoco captioned the same video on her social media.

Cuoco, who was named the second highest-earning TV actress in the world by Forbes this year, was previously married to tennis player Ryan Sweeting; the pair finalised their divorce last May.