The Tottenham star is expected to move to Real next week.
"I asked the club to buy him [Bale] last season but it was not possible," Mourinho told ESPN.
"It looks like it is happening this season so I am happy for them because they have got a fantastic player but, of course, the numbers are huge numbers and the kid has to go now and there's pressure to prove that he's worth that investment.
"I think he's a fantastic player and the way my Real Madrid was playing, I think it was an easy player to fill a space and to get into that tactical dynamic.
"I don't know what Carlo [Ancelotti] is thinking now but Carlo is an experienced coach and for sure will get the best out of him."