The 18-year-old has now made that move, but not before penning fresh terms with the Gunners.
As an exciting prospect to have graduated through the academy ranks in north London, Nelson says it was always his intention to extend his stay with Arsenal.
He told the club’s official website: “It’s my boyhood club.
“From a young age, from about eight years old, I’ve been supporting the club.
“The likes of Thierry Henry have encouraged me as well, so ever since then I’ve just loved the club and really fell in love with it.”
Arsenal will be hoping to see the youngster return to England next summer ready to push for a regular place in their senior side.
A spell at Hoffenheim is intended to aid that development, with Unai Emery happy for Nelson to go in search of game time elsewhere.
He said: “Reiss is a talented young player and we’re pleased that he has signed a new contract with us.
“This move to Hoffenheim will give him the chance to get regular high-level competition in the Bundesliga and is an important step in his development.”
Nelson made 16 appearances for Arsenal under Arsene Wenger last season, having made his competitive debut in the 2017 Community Shield.
Only three of those outings came in the Premier League, though, with it now up to him to prove in the Bundesliga that he is capable of gracing the grandest of domestic stages.