Amy Smith said ‘‘yes’’ at Greater Union Shellharbour cinemas after long-term beau Liam Cooper staged an ultra-elaborate big screen proposal almost six months in the making.

The unsuspecting Miss Smith sat down to a movie as part of a ‘‘double date’’ on March 14, before Mr Cooper got up ‘‘to use the bathroom’’. 

A group of 50 friends and relatives piled into the theatre as Mr Cooper appeared on the big screen and, set to the Magic! song Rude, began delivering his proposal.

Mr Cooper, a seasoned multi-instrumentalist, songwriter and performer well known to Illawarra audiences, drew on skilled collaborators including cinematographer Kieran Hoyle and former Southern Stars creative director Katrina-Jane Cameron to craft the high-quality video.

There were months of planning meetings, filming, editing and even a trial run at a cinema in Bondi Junction to ensure the technology would work.

‘‘There was a huge number of favours pulled in,’’ Mr Cooper, 23, said. 

‘‘Because we have been dating for so long and talking about getting married, if I’d just taken her on a romantic dinner or a hot air balloon ride, she’d [know] right away, wouldn’t she?

‘‘This way it was something she would not see coming.’’ 

The video was released to Youtube on Wednesday and has since been viewed more than 20,000 times.

It shows Ms Smith laughing at the video before the music dies away and Mr Cooper returns to the cinema in person to pop the question.

‘‘It’s so embarrassing,’’ she says, before a nod and a ‘‘yes’’.

The couple met through a youth group attached to Figtree Anglican Church, and have been dating since they were teenagers.

They are planning November nuptials in Berry.

According to Mr Cooper the wedding will be a more low-key affair than the proposal.

‘‘It will be a relatively small wedding with friends and family - we’re very excited,’’ he said.