Director Gary Cook had filled the other five parts but was finding it hard to cast the eccentric idealist.
Gavin, 44, thought he had missed out, as auditions took place during the mandatory four weeks he was nearly 4,000 miles away in Kampala, before marrying long-term partner Connie there on December 20.
A global talent manager for the American-based digital health consultancy BOLDSCIENCE, he has drama experience stretching back 30 years to when he was a child actor with the Argosy Players in Ruislip, Middlesex.
He also has a BA degree in theatre practice and was keen to get involved with the Players as he and Connie are looking to set up home in Brighton.
Gavin said: "I'd written it off, as the production was almost fully cast but mentioned that if by any chance there were any parts left, I would be prepared to audition online."
Gary, Players president Debbie Creissen and artistic liaison Giles Newlyn-Bowmer came up with a way to watch Gavin go through his paces online from sunny East Africa, on the eve of his wedding, no less.
Gary said: "I was stumped on the casting of Simon and after filling the other five parts was reminded by my producer, Debbie, that Gavin had contacted us with a view to getting involved.
"Long story short, I contacted him to arrange a Zoom call and he gave a great audition. In conversation, I asked him whereabouts he was. He said he was talking to us in Africa.
"Ah, I said, is that a holiday or work? Turns out he was getting married the very next day. We were able to notify him that he had the part on his wedding day."
The wedding was 'beautiful', an outdoor ceremony at the Explorers Hub hotel in Kampala, with friends and family celebrating in the sunshine with a huge barbecue. And despite everything else going on, Connie was supportive with the audition.
Gavin said: "I must admit that I wondered if I really needed the pressure. I had so much on my mind before the big day, not least trying to remember my bridegroom's speech! Also, I'd received the audition piece only three hours before but Connie was great in helping me with my lines."
Connie works for a charity helping underprivileged children in East Africa and met Gavin four years ago in Zanzibar, where they were travelling with different groups of friends.
Gavin said: "We had parties on the beach and got to know each other there. We messaged each other after the holiday and travelled together on other trips to places like Kenya, Zanzibar again and Tanzania."
Southwick Players will perform Torben Betts' black comedy Muswell Hill at the Barn Theatre, Southwick, from April 10 to 13, at 7.30pm. Box office 0333 666 3366 or book online at southwickplayers.org.uk