The pin-up-turned-reality TV star's longtime director boyfriend Nick Carpenter recently popped the question and Marquardt took to Instagram.com on Thursday (01Oct15) to share the happy news.
The blonde beauty posted a snap of her hand in his, showing off her unique spider-shaped diamond engagement ring, along with a sign in the background which reads, "Till Death Do Us Part".
"Happy Oct. 1st!!!," she wrote. "Oh...and... Did I mention @nicholascarpenter and I are engaged?"
Marquardt and Carpenter first met at the Playboy Mansion, where she lived with Hefner and her The Girls Next Door co-stars Kendra Wilkinson and Holly Madison.
They began dating in 2008.
This will be Marquardt's second marriage - in 2007 she revealed she was separated from her first husband, who remained one of her closest friends.
Her fiance is the son of astronaut Scott Carpenter.