The Holland international will join Barca this summer for a fee rising to €86m.
Bartomeu said: "About the case of Frenkie De Jong. When we fought for him to come to Barcelona and we thought he could choose not to come, we decided to fly out and explain to him and his family about Barça, and other things like the city and the club that we could offer him.
"We also explained that his decision would change his life forever. Not only in his case, but in that of all the players who decide to join us."