The former Bachelorette contestant – who came in second on Ali Fedotowsky's season – is engaged to fellow reality star Peyton Wright, his rep confirms to PEOPLE.
Lambton, 34, proposed to Wright, 28, a past Bachelor and Bachelor Pad contestant herself, with a David Yurman round cut diamond ring on Saturday at his house in Cape Cod.
"I knew it the first day I met her – she walked in and I was like, 'Oh, my God,'" Lambton tells PEOPLE of Wright, whom he met through fellow Bachelorette contestant, Jesse Beck.
"Everything happens for a reason!" he adds of the way they met.
The couple, who have been dating since August 2010, will "just enjoy being engaged" for a few weeks before they begin to plan their wedding, he says.
"It's one of those things where I've had a ton of serious relationships and I met this kid and he was genuine, outgoing and hilarious and we just click," Wright said in January.
On his season of The Bachelorette, Lambton was a favorite, but narrowly missed out on Ali's final rose.