Mel wore a sleek blue suit, but his real style statement was his long, scruffy salt and pepper beard. Milo wore a black suit and also sported some thick facial hair.
Hacksaw Ridge, which hits theaters on Nov. 4, marks Mel's return to directing after nearly a 10-year hiatus, and will be the first time he's directed his son, who takes on the role of Lucky Ford in the movie.
Milo is the Braveheart star's fifth child with ex Robyn Denise Moore. The two have seven children total and Mel has a 6-year-old daughter, Lucia, with ex Oksana Grigorieva. He is also expecting his ninth child with girlfriend Rosalind Ross, and spoke to ET at Monday's event about having another child at 60.