The pair, who starred alongside each other in MTV's The Hills, were pictured at the nuptials and both oozed sophistication in their pretty but simple outfits.
Lauren wore a short navy dress to event, while best friend Lo opted to flash some cleavage in a black maxi dress with plunging neckline. Swit swoo!
Throughout the day, Lauren posted several photographs on Instagram - including the shot of herself and Lo - and one of hers and fiancé William Tell's place cards.
Lo, meanwhile, uploaded a picture of herself, Lauren and their pal (thought to be the bride) ahead of her big day. She said: "Our best friend's wedding!!!! @laurenconrad #oehmsweetoehm."
We're guessing Lo (whose real name is also Lauren) meant 'home sweet home', so presumably the wedding was held in Laguna Beach, California, where the girls grew up.
In fact, that was even the place where they both found fame, after starring in MTV's Laguna Beach: The Real OC while in high school!
Although Lauren is still based in California, Lo now lives in New York, so the wedding was the perfect opportunity for them to catch up with each other.
Reflecting on the day while sipping on a drink, Lo posed for a funny picture the morning after the night before, which Lauren posted online. She joked: "Ladies and Gentlemen, Lauren Ogilvie Bosworth."
Hopefully we'll be seeing more wedding pictures of these two very soon, as Lauren is due to tie-the-knot with William in the autumn!
Laguna Beach: The Real OC - Where are they now?