James Franco says his brother Dave and his fiancée Alison Brie are "so in love" and their wedding will be "so romantic."

James Franco

James Franco

The 37-year-old actor couldn't help but gush about his younger sibling, 30, and soon-to-be sister in law as he commented on their strong bond and future nuptials.

Speaking to PEOPLE magazine, he said of the happy couple's impending big day: "It's going to be really romantic."

He added: "They are so in love. They just love each other."

Dave and Alison, 32, who are notoriously private, got engaged in August following three years of dating but are yet to divulge the details surrounding their wedding day.

The loved-up couple sparked rumours they were heading for the aisle when the stunning actress was pictured wearing her new engagement ring at a screening of her new movie 'Sleeping With Other People' in Los Angeles in the summer.

The pair prefer not to speak about their relationship and are rarely pictured together, even choosing to walk the red carpet separately at this year's Met Gala.

However, Alison recently admitted she's so pleased she's found someone who is so "incredible in every way."

She said: "I have an incredible fiancé. He's so wonderful. He's just the sweetest man I know. And he's so funny and incredible in every way."