David first shared a cute throwback snap of himself holding Brooklyn on the day he was born.
"So on this day 18 years ago this little man came into our lives.... To say we felt blessed is an understatement," he wrote. "From day one he never slept through the night the only way he would fall asleep is when I took him out in the car and it had to be BoyZone on the radio and he would drop right off.... Thank fully he now sleeps the whole night without needing a song."
"Brooklyn has gone from this beautiful baby boy to become this handsome , polite and driven young man .. I'm proud that he lived through my career with me and I'm even prouder about the person that he has become," he continued. "Happy birthday Bust you can now officially take dad for a drink down the pub X ❤ @brooklynbeckham@victoriabeckham."
Victoria, meanwhile, shared a sweet slideshow of her firstborn.
"I can't believe our baby is 18 today. We are all so proud and love u so much @brooklynbeckham x Happy Birthday Buster x Lots and lots of love x," she wrote before sharing another cute pic of Brooklyn as a kid.
"I didn't actually know that they were big until I was about 13," he told Wonderland. "I went to a football game and people were shouting my dad's name and I was like, 'What?! Oh my God.' I don't look at them like that."