Southampton sealed the £18M transfer on Tuesday and broke the news at their PUMA kit launch in the evening, surprising fans with how quick the reveal was.
Premier League rivals Ipswich Town who was also recently promoted were prepared to match Southampton's offer to West Ham but Downes opted to return to the Saints.
Martin spoke about how worried he was about the transfer and his relief when Downes chose his club.
"There was a moment where me and Matt Gill thought it might not happen and it went dark for a few hours.
"Thankfully, Flynn saw the light and he’s now here. It’s been amazing, great seeing him back. It’s still so early in pre-season as well.
"I think everyone, the staff, the players and the fans are so pleased to see him. He is ours now and that is the best thing."