The Dane, just 33 years old, will take over the under-23 side, who play in the fourth tier of German football, for the 2019/2020 campaign.
He will replace Alen Terzic, who is currently in interim control after Jan Siewert departed to take over Huddersfield Town earlier this season.
Tullberg will leave Danish first division side Vendsyssel FF where he has been assistant coach for the past two seasons.
“It’s a job opportunity you don’t get many times during your coaching career and I’m proud that as a Danish coach I get the opportunity to become a coach in one of the biggest clubs in Europe,” he told Vendsyssel official website.
“I am incredibly grateful for the chance that Vendsyssel FF has given me. This is the first time I’ve been a coach for a senior team and I’ve learned a lot and met some amazing people. At the same time, it has been a pleasure to see how the club has developed since the summer.”
Tullberg signed for Hearts in the 2008-2009 campaign after impressing then manager Csaba Laszlo on trial, signing from Italian side Reggina. However, he was plagued with injury issues and played just seven times in a season which saw Hearts finish third and qualify for Europe.
In 2012, after a spell with German side Oberhausen, he had to retire due to ongoing knee problems.
The former striker moved straight into coaching becoming assistant at SG Schonebeck before a move back to Oberhausen to coach the junior teams up to the U19s for four years,
Tullberg returned to Denmark to coach the U19 side for former club Aarhus GF which led to his current position at Vendsyssel FF.
Recent managers of the Dortmund reserve team have gone on to manage Huddersfield Town, Norwich City and Hamburg.
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