Nicole Richie is reportedly furious over her fiance’s friendship with Mary-Kate Olsen. The 26-year-old socialite is believed to have told Good Charlotte rocker Joel Madden, 29, to stay away from the actress after she was seen flirting with him at a recent dinner.
A source said: "During the dinner, Mary-Kate was very playful with Joel. It was all fun and games, but with the Olsens nothing is as simple as that. Nicole exploded at Joel and demanded that they leave the party. Afterward, Nicole warned him to stay away from Mary-Kate.”
Mary-Kate, 22, went to watch the rocker perform in New York last week, further angering Nicole – who gave birth to the couple’s first child, daughter Harlow, in January – by hanging out with the band after the show.
The source added to Life and Style magazine: "After the concert, Joel invited her back to see the tour bus. He showed her some baby photos of Harlow. Joel isn't one to lie or hide things from Nicole, so the next day he told her about it on the phone.
“Nicole freaked out. Joel thought she'd respect the fact that he was trying to be honest - after all, he and Mary-Kate are just friends - but Nicole was hurt and angry. He couldn't deal with it, so he hung up, and she kept texting him after that."
The argument is said to be the latest in a series of rows between the couple, resulting in them putting off setting a date for their wedding.
The insider claimed: "They're having their usual ups and downs. I think they're madly in love and want to get married. But I also think it's moments like this that will continue to keep their wedding on hold."

Nicole Richie is behind a new online gift registry that will provide baby products to moms in need. Richie will launch the Web site this fall through her Richie-Madden Children's Foundation, the charity she and boyfriend Joel Madden started last winter when she was pregnant with daughter Harlow.
"Nicole saw that even a clean blanket was out of reach for some of these new moms so she wanted to figure out an efficient way to connect them with companies and individuals who want to help," foundation advisor Bruce Richman tells PEOPLE.
The registry will start off helping families in the Los Angeles and New York areas before expanding throughout the country and internationally.
"We take for granted the basic necessities. For some families, it's a serious struggle," Richie tells PEOPLE. "This is one way to ease the financial burden, and help new babies have a good start in life. We are only working with companies and products that Joel and I would use. We're checking every product out for safety – and all products are BPA-free."
Here's how it will work: Families will sign up through local social service agencies. A list of baby products they need – such as cribs, strollers or blankets – will be posted on the Web site. Donors can view the wish-lists and choose what to contribute (much like a wedding or baby gift registry).
Richie and Madden hope to feature baby products that they would use with their own daughter, 7-month-old Harlow. The foundation is still lining up sponsors for the as-yet unnamed registry site, which is being guided by DonorsChoose.org and Baby2Baby.org.

August 14 - With Ashlee Simpson’s due date looming closer and closer each day, it’s important for her to surround herself with women who can help her get ready for motherhood. And Nicole Richie looked to be passing on a few pearls of wisdom to the “La La” singer. The new mommy and the mother-to-be were spotted enjoying an afternoon of shoe shopping at Barneys New York in Beverly Hills before heading out into the residential areas to do a little house hunting.

August 13 - Nicole Richie arrives at traffic school in Los Angeles (+31) (hq).

August 8 - Nicole Richie in shorts and trendy boots at Cafe in West Hollywood with a friend (hq).

August 6 - Nicole Richie arrives at traffic school in Los Angeles.

August 5 - Nicole Richie and Joel Madden out in West Hollywood.

Nicole Richie has banned fiance Joel Madden from getting another tattoo.
The 26-year-old beauty, who has a six-month-old daughter Harlow with the Good Charlotte rocker, reportedly lost her temper when Joel told her he wanted an etching of their daughter on his tooth.
A source said: "Joel promised Nicole that he wouldn't get any more tattoos. Then a friend suggested a tooth tattoo, which is a photo imprinted on a tooth. When Joel told Nicole he wanted to get their daughter Harlow's face tattooed on one of his front teeth, she shrieked, 'Absolutely not!' "
Tooth tattoos are tiny, detailed portraits made on crowns and placed over the tooth. They can cost up to $500, but can be easily sanded off by a dentist if necessary.
Joel currently has around 10 tattoos, most of which completely cover both his arms.
The first etching he and his twin brother Benji ever got was of an Irish flag just above the elbow.

July 25 - Nicole Richie visits her friend (hq).