Answer based on context:

Hoping to rebound from their divisional home loss to the Patriots, the Jets flew to Qualcomm Stadium for a Week 3 MNF duel with the San Diego Chargers.  In the first quarter, New York took flight as CB David Barrett returned an interception 25 yards for a touchdown.  The Chargers responded with kicker Nate Kaeding getting a 36-yard field goal, along with QB Philip Rivers completing a 1-yard TD pass to FB Mike Tolbert.  In the second quarter, San Diego increased its lead with CB Antonio Cromartie returning an interception 52 yards for a touchdown.  The Jets answered with QB Brett Favre completing a 3-yard TD pass to WR Laveranues Coles. The turning point in the game occurred on the following kickoff, an on-side kick, which traveled only 15 yards before the Chargers picked up the ball. They then added a touchdown, with Rivers completing a 27-yard TD pass to WR Chris Chambers. Following another interception, the Chargers scored again with a 6-yard TD pass to TE Antonio Gates. In the third quarter, San Diego increased its lead with RB LaDainian Tomlinson getting a 2-yard TD run. New York then managed to move the ball down to the San Diego 9-yard line, but turned the ball over on downs.  In the fourth quarter, New York tried to rally as Favre completed a 4-yard TD pass to WR Chansi Stuckey (with a failed 2-point conversion), along with kicker Jay Feely getting a 32-yard field goal, yet the Chargers answered with Tomlinson's 2-yard TD run.  Afterwards, the Jets tried to make yet another comeback attempt as Jerricho Cotchery ran a return ball 54 yards. Favre completed a 13-yard TD pass to TE Dustin Keller to put them within 2 touchdowns from tying, yet San Diego sealed the win with Kaeding's 49-yard field goal with 2:08 left in the game.

How many yards was Favre's longest TD pass?
13