Jessica Simpson's fiance Eric Johnson shared a rare glimpse of the couple's son Ace, 4 months, while arriving at LAX airport on Friday, Nov. 22 Credit: HGVC/AKM-GSI

On baby duty! Jessica Simpson's fiance Eric Johnson is one adorable daddy. The former NFL player shared a rare glimpse of the couple's 4-month-old son Ace when he stepped out to board a flight at LAX airport on Friday, Nov. 22.

During the outing, Johnson, 34, is seen trying to keep a low profile while holding his baby boy. Johnson goes casual in jeans, a blue t-shirt, an open button-down, and a baseball cap. He also shows off some extra scruff. Meanwhile, his sweet little boy wears a matching blue button-down, a vest, khaki pants and brown booties.

One week earlier, Simpson's hubby-to-be was also spotted bonding with their daughter Maxwell, 19 months. At the time, the father-daughter duo headed to the Calabasas Commons to pick up burgers and milk shakes from Johnny Rockets on Nov. 15.

Simpson, 33, and Johnson have been quite protective of Ace since welcoming him in June, only showing him off a few times in public. In August, the former Fashion Star mentor exclusively debuted their little bundle of joy on the cover of Us Weekly for its Sept. 9 issue. One month later, she celebrated Ace turning 3 months old by sharing black and white pictures of the bouncing boy via Twitter on Oct. 5.