Robert Pattinson and FKA Twigs marriage may be in trouble. According to reports, the "Twilight" star may be cheating on FKA Twigs with Sienna Miller. In recent interviews, FKA Twigs said it can be hard to date a celebrity, especially when Twilight fans want to see Robert Pattinson reunite with Kristen Stewart.

Robert Pattinson first rose to fame as vampire Edward Cullen in the movie adaptation of Stephanie Meyer's "Twilight" series, in which he co-starred with his then-girlfriend, Kristen Stewart.

Celeb Dirty Laundry reported that Pattinson was seen flirting with his "Lost City of Z" co-star Sienna Miller.

In Touch Magazine reported that Robert Pattinson and Sienna Miller are spending a lot of time together without FKA Twigs and people are beginning to notice their constant flirting. Star Magazine reported Pattinson and Sienna Miller are "spending a lot of time hanging out in each other's trailers" on the set of "The Lost City of Z."

Sienna Miller used to hang out with Pattinson and Kristen Stewart while they were still dating.

Sienna and her now ex-husband Tom Sturridge introduced Pattinson to FKA Twigs. Sienna Miller and Tom Sturridge split up on July 2015 after four years together.

Recent reports say Pattinson and Twigs relationship is in trouble too. Robert Pattinson and FKA Twigs reportedly got engaged Coachella 2015 in April this year.  Sources told People Magazine that Pattinson and Twigs put their wedding plans on hold.

While Pattinson and Miller have always maintained that their relationship is platonic, this isn't the first time rumors have surfaced about their friendship.

The "Twilight" actor defended his fiancée in a recent interview for NME. Pattinson said he doesn't get why some people enjoy another person's reputation.

"I think it's because most normal people are not commenters," Pattinson told NME.

"I've never met anyone who's left a comment on anything. It's just demons who live in basements. You have this weird thing where you end up trying to fight against this faceless blob, where the more you hate it, the bigger it gets, because it's all in your head."

Pattinson told NME that Twigs was "just an amazing, amazing artist," but did not discuss their relationship.