The Brazil-born centre-half was drafted on Monday into the Oranje party for the World Cup qualifiers against Andorra and Romania.
And he felt it was justification for turning his back on his native country and pursuing an international future with Holland.
He told ANP after his first training session on Monday: "I'm very happy, this is such a special, special day.
"I had to do so much to become a Dutch citizen. I'm glad I'm here now, I've studied hard.
"It has lasted about three years and everything was difficult. But now my Dutch is a lot better and I know a lot of the country."
The 24-year-old is now hoping to make a positive impression in front of coach Louis van Gaal.
"My goal was always to be called up by the Oranje," Douglas added.
"Now I have to make sure that I stay here for a long time. I must do this by continuing to work hard, especially in the coming days.
"I will do everything to show that I deserve a place in the squad."