Jared Harris is engaged to his long-term girlfriend, Allegra Riggio.

The former 'Mad Men' star, 51, and his 38-year-old fiancee are ''giddy and adorable'' after he popped the question with a heart-shaped rose-gold diamond ring, with a mounting in the shape of the letter 'H' for Harris, by Erica Courtney on Sunday (02.06.13).

The brunette beauty, who is a TV host and contributor to beauty website XOVain.com, shared her engagement excitement on Twitter, writing: ''We're engaged. #TeamHarris.''

She later responded to congratulatory messages, writing: ''SOOOOOOOO HAAAAAAAPPYYYYYYYY AAAAAAAA!''

In a message to another fan, she wrote: ''THANK YOU!!!!! We're giddy and adorable.

A source confirmed to E! News that Jared proposed on a beach in Malibu at sunset.

The couple, who met almost four years ago at a comedy show, announced the news to friends, who gathered at Bar Lubitsch in Los Angeles for Allegra's 38th birthday on Monday night (03.06.13).

Jared, who is the son of late Irish acting legend Richard Harris, most recently appeared on the big screen playing Ulysses S. Grant in Steven Spielberg's 'Lincoln' and will next star in the action-adventure fantasy, 'The Mortal Instruments: City of Bones', due to be released in August.