The Portugal international died in a fatal car crash with his brother when their Lamborghini suffered a tyre failure, veered off the road, and burst into flames.
Speaking at the event, the Portuguese coach shared a heartfelt tribute to the late striker.
"When people leave this world, normally we all say 'such a nice guy'. Diogo was really a nice guy," Mourinho told Sky Sports.
"He had my agent (Jorge Mendes), so of course I knew a lot about him. And people in Liverpool know what I’m saying is true. He is a kid who nothing was easy for him, he had to fight to arrive where he arrived.
“Three kids without a dad, a young woman without her husband, the parents lose both sons…it’s crazy. It’s difficult to understand. Maybe one day we will understand but not now."