Former Leinster star Brennan played all 100+ minutes of the try-less 2004/05 European decider, staged in front of 51,000 spectators at Murrayfield, putting in an outstanding display up front as France fly-half Frederic Michalak emerged as the Toulouse hero.
He kicked a penalty eight minutes into injury-time to level things up at 12-12 and send the final into extra-time for the first time, in the tenth year of the ERC's flagship tournament.
Michalak then popped up again in the second minute of the first extra-time period to fire over his second penalty, and the 22-year-old kicked a clinching 35-metre drop goal in the second period to ensure the south of France side's history-making third European title.
Brennan's good friend Gareth Thomas, who lined out in the Toulouse number 11 shirt, also became the eighth Welshman to claim a Heineken Cup winners' medal.
The Wales captain was the sole 2005 British and Irish Lion on view.