John Stamos is mourning the loss of a dear friend ... announcing the heartbreaking news on social media Monday.

The Full House alum’s longtime pal and “brother,” Mike Owen, recently died of a “sudden heart ... surreal and devastating.” Related: John Stamos Vows to Stand with Dave Coulier 'Through ...

John Stamos is reflecting on the people who mean ... who had been best friends with Stamos since they were 11. Owen died in November from a heart attack. “To Mike, my oldest and dearest friend ...

Caitlin McHugh knows she married a Hollywood heartthrob. John Stamos’ wife joked about the “Full House” actor’s romantic history in an interview with Fox News Digital published Tuesday.