Are Dakota Johnson and Chris Martin expecting their first child together?

UPDATE: Johnson's rep denies that she is expecting a baby, telling People that the "Fifty Shades" actress was simply celebrating her birthday, which was on October 4.

Dakota Johnson and Chris Martin are reportedly expecting their first child together.

TMZ reported on Monday that the uber-private celebrity couple held a star-studded gender reveal party at Martin's Los Angeles home on Sunday, where the couple announced to friends like Julia Roberts and Sean Penn that they're expecting a baby boy.

The alleged news comes a year into the pair's relationship and, interestingly, just a week after Martin's ex-wife, Gwyneth Paltrow, married Brad Falchuk, her boyfriend of four years in the Hamptons.

Photos and videos from outside of the event show two separate balloon arches -- one blue, one pink -- floating above the backyard before the strand of blue balloons was released into the sky, seemingly revealing that they're expecting a boy together.

Also there were Johnson's parents, Melanie Griffith and Don Johnson, who arrived late.

The couple has never walked a red carpet together, but they have attended the same events -- most recently at the Global Citizen Festival in Central Park at the end of September, where Martin performed and Johnson presented while wearing an auburn slip dress under a heavy topcoat -- despite soaring temperatures.

Dakota Johnson's most recent outing at the Global Citizen Festival on September 29, 2013. (Getty)

Martin shares daughter, Apple, 14, and son, Moses, 12, with Paltrow.