Madden Bro Back on the Market (E! Online)

Los Angeles (E! Online) - Benji Madden may still be rocking, but his fiance has rolled.

In the wake of increasing trouble-in-paradise-type speculation for the Good Charlotte guitarist and Australian singer-actress Sophie Monk, the Down Under stars rep has confirmed that the formerly betrothed twosome has uncoupled.

Sophie and Benji have officially split, Yoon Kim, Monks Sydney-based agent told the Daily Telegraph. The decision was mutual and they remain amicable. This will be my only statement regarding this matter.

The camera-ready couple, often spotted on double dates with Maddens band mate brother Joel and his fiance, Nicole Richie, had been together for 18 months. They first met in the summer of 2006 on the set of a Good Charlotte music video.

Just six months later, on Christmas Eve 2006, the 28-year-old Madden popped the question to Monk, also 28, at her familys tony Gold Coast home. He sealed the deal with a bauble from Neil Lane.

Reports of a rift between the comely couple began over the holidays, when Monk canceled an appearance at an Australian event, Carols by Candlelight, at the last minute, citing the ever-mysterious family reasons.

The pull-out followed a widely criticized Down Under red carpet-hosting gig by Monk, raising eyebrows over a possible cause for her distractedness.

Late last month, Monk, who got her start on Australias Idol-esque reality-competition show Popstars before appearing in the films Click and Date Movie and HBOs Entourage, was photographed in Los Angeles sans engagement ring. She has since returned Australia.

But while one Madden brother is back on the market, the other is way off.

The five-minutes-older Joel, along with Richie, welcomed daughter Harlow Winter Kate Madden in Los Angeles Jan. 11. The nesting duo emerged from their domestic cocoon just this past weekend, hitting up a bevy of social scenes, including the opening of LACMAs Broad Contemporary Art Museum, at which new grandpa Lionel Richie performed.