Lanter, 29, proposed to his girlfriend of three years, Angela Stacy, in May 2012, while Grimes, 23, announced her engagement to musician Josh Beech in December 2012. The costars -- whose characters were once romantically involved -- have been swapping wedding planning tips in between takes in California.
"On set we've been on and off like, 'What are you doing?' And I'm learning, too. I'm trying to plan my wedding as much as I can be involved, and I'm asking Shenae what's up with her, what kind of colors is she doing," Lanter told Us Weekly at a W Magazine and Guess event in West Hollywood Jan. 8. "I know all these crazy details about weddings that I would have never have thought of before, but I do now."
Lanter and Stacy are planning to tie the knot in the fall of 2013; Grimes recently said that she and Beech "plan to keep our special day very private."
The actors' real-life romances aside, Lanter said fans are still pulling for his character, Liam Court, to rekindle his relationship with Grimes' Annie Wilson. "There are some Liam and Annie scenes coming up -- some really really interesting ones," the actor teased.
"It's awesome to have that support," he told Us. "I don't know why [they're so fervent]. Me and Shenae joke about it all the time. We're like, 'We don't know why these fans want us together?' Because me and her, we have like a brother and sister relationship. We make fun of each other and pick on each other all the time, so it's kind of funny that the fans see that as this ultimate chemistry."
90210 airs Mondays at 8 p.m. EST on The CW.