Van den Berg left Liverpool for the Bees in August.
He told the Brentford website: "Liverpool wanted me to stay, but I knew what I wanted. I wanted to go somewhere where I play every week.
"I was lucky that there was a lot of interest, but that also made it a little difficult. It was a luxury problem.
"Brentford was one of the first clubs to show interest and I wanted the chance to play in the Premier League and live in London.
"I spoke with Thomas Frank. In the first meeting he asked me direct questions. 'Why do you want to play for Brentford? Why do we need you at Brentford?'
"It was so direct. It was a real job interview."
Frank kept in touch with the defender over the coming weeks.
"Subsequently, Thomas and I had many calls and messages.
"He called me every two weeks and we talked over WhatsApp. He's just a really nice person.
"The football part must also be the right thing, and it is. But Thomas really made me feel they wanted me here."