The Boston Celtics star is expecting his 4th kid with wife Robyn -- and after that lackluster gender reveal moment back in 2018 ... ya gotta feel stoked for the guy!

Remember, back in July 2018, Robyn revealed to Gordon that she was pregnant with a little girl ... making it 3 girls to 0 boys.

Gordon's reaction was priceless ... a look of disappointment -- followed by that infamous line, "Daddy's always happy."

Of course, Hayward is happy to be a #GirlDad, but now he's got ANOTHER kid on the way -- and this one is a male. In other words, Gordon got his wish!

Robyn and Gordon, who are very self-aware, made a joke about the gender reveal ... posting, "Baby G coming in September *** yes, it’s a boy."

So, congrats to the whole Hayward family ... and to the fetus -- no pressure kid!