Uh-oh! Robert Pattinson and FKA Twigs' wedding might not be happening soon. Based on the latest reports, the engaged couple are having issues with each other's demands, particularly inserting Pattinson's ex, Kristen Stewart into the picture.

Following their breakup in 2012, former "Twilight" couple Robert Pattinson and Kristen Stewart have been incessantly linked to each other in spite of living their separate lives. Now, Stewart's name is once again dragged into FKA Twigs' wedding preparations.

Earlier this month, Twigs reportedly gave her 29-year-old fiancé an "ultimatum" about setting the date of their wedding. According to Celeb Dirty Laundry, the 28-year-old English songstress has demanded that Pattinson will choose a wedding date within the year or their relationship will fall apart.

"Twigs has told Rob this year they have to get married," an insider said, as per Hollywood Life. "She's fed up of waiting, and she wants something small, quiet and private, so it doesn't need any elaborate plans."

Contrary to what many fans and showbiz watchers believed to be a lavish event, Robert Pattinson and FKA Twigs' wedding will be a "small affair" with only their family and friends in attendance, Inquisitr noted.

"It may even be a registry wedding, in front of a handful of friends and family in the U.K.," a source added. "She's told him she would like to do something in the summer, but has warned him she doesn't want this dragging on."

Robert Pattinson, on the other hand, has his own set of demands. In fact, several reports claimed that he demanded to put ex-girlfriend Kristen Stewart on the guest list.

Furthermore, the "Life" actor also told his fiancée to minimize her jealousy fits and accept that Stewart will always be an "important part" of his life.

Meanwhile, Kristen Stewart is not the only one to blame for the delay in Robert Pattinson and FKA Twigs' wedding. Design & Trend reported that Pattinson's family is also causing the delays after they questioned if Twigs' is the right woman for him.

"They planted a seed in his head, questioning whether Twigs is the right person he should be settling down with," a source explained. "He just wants to make sure everyone in his family is on the same page. It's like, even after all this time, he still has to convince them that Twigs is the right girl for him."

While Pattinson's friends added that the "Map to the Stars" actor misses his "wild life" with Stewart.

In other news, fellow "Twilight" star Kellan Lutz recently got candid about his thought on the upcoming Robert Pattinson-FKA Twigs' wedding. Despite being friends with Pattinson, Lutz revealed that he unsure if he'll be invited to the nuptial.

"I love the guy to death and we always hang out when he's in town or I'm in town," Lutz said. "I'm sure he's going to be super selective [about the guest list]. I might text him after this and say 'Hey, if you're ever thinking about tying the knot, you better make sure I'm there.'"