Senna, widely regarded as the greatest racing driver of all time, died when his car careered off the Imola track in the early stages of the San Marino Grand Prix on May 1, 1994. (Agencies)
He was 34 years old. It was Formula One's blackest weekend which also saw Austrian rookie Roland Ratzenberger killed and Senna's compatriot Rubens Barrichello injured.
"When I was a kid I had all the books, all the videos, he was the driver I looked up to," said Hamilton, who was just nine at the time of Senna's death.
"He inspired me to be a driver and on the day of his passing, his death was... it was very difficult for me to show my emotions so I went off to a quiet place and it was very difficult for several days to really... your hero's gone."
Senna, the outspoken world champion of 1988, 1990 and 1991, was leading in San Marino on lap seven when his Williams car veered spectacularly off the racing line at 190mph (307km/h) at the Tamburello corner and straight into a concrete wall.
He received emergency treatment at the scene before being airlifted to Bologna hospital where he was later declared dead.
"He was an incredible legend. You like to think that one day you may be recognised as someone that was able to drive similarly to him," added Hamilton, the 2008 world champion.
Alonso, the 2005 and 2006 world champion, was 12 when Senna was killed and the Spaniard vividly recalls the day of the tragedy.
"On my schoolbooks I didn't have pictures of girls, obviously I was too young but I had Ayrton there and the same in my room," said the Ferrari star.
"I had a big poster of Ayrton and even my first go-karts were in the colours of Ayrton's McLaren because my father also liked him. It was a very sad moment," he said.
Senna, widely regarded as the greatest racing driver of all time, died when his car careered off the Imola track in the early stages of the San Marino Grand Prix on May 1, 1994.