Matthew Lawrence, who costarred with Robin Williams in "Mrs. Doubtfire," says the late actor opened up to him about the dangers of substance abuse.

Matthew Lawrence opened up to PEOPLE about why he dedicated his 'Masked Singer' performance of "Hallelujah" to his 'Mrs. Doubtfire' costar Robin Williams.

"And then on top of that, you get a chance to be around Robin Williams and he takes an investment in you, as he does with people. But in particular, he really took an investment w