Tom Cruise & Helen Mirren On Hand to Celebrate Queen's Platinum Jubilee

Queen Elizabeth II may not show for every public event these days, but made sure to come out for this one to celebrate 70 years on the throne ... as did Tom Cruise and Helen Mirren.

HMTQ was on hand in person Saturday for a Windsor get-together called A Gallop Through History -- which is essentially a giant horse and pony show meant to reenact Liz's ascension to the throne ... via onstage performances and feats featuring animals.

That's where TC and the Dame herself come in -- they were tapped to help do the theater part of this whole thing, and Tom made a splash when he touched down for grand entrance earlier in the day.

Unclear what role exactly he's playing in the play, but Helen was assigned Queen Elizabeth I ... and apparently killed her performance, with a rousing speech that stirred the crowd.

Anyway, QE2 seemed pretty thrilled by all the pomp and circumstance ... she was cheesing from her seat watching all the activity down below. The Queen looks great, which is encouraging to see considering her health of late has been a bit touch-and-go.

Like we said, this is one of the bigger events that have been held for her Platinum Jubilee -- which has been going on since February and ends in June. So, yeah ... she's a trooper.

Liz is 96, and while she might not be as out and about as she once was ... it's clear she'll go the extra mile for a special occasion such as this.