He led the extermination of the Klingons working on the colony on the world of Khitomer in 2261 with new weapon systems provided by Section 31. He then rejoined the Romulan fleet in the Hectori sector after consulting with one of the Section 31 agents.
After rejoining the fleet near the Romulan/Klingon border, L'Nar was then met once again by a Section 31 agent who had a fleet of advanced ships that eluded L'Nar's ships' sensors. L'Nar and the Section 31 then saw that the Klingons had redeployed their fleet to defend their colonies. Both saw it as a opportunity to attack Qo'nos. Both L'Nar's and Section 31's ships bombarded Qo'nos's main cities.
L'Nar then had Capt. Kirk and his landing party brought aboard his ship, the IRW Raptor One, as guests of the Romulan Empire. L'Nar's forces then came under attack by the the Klingon's new D7-class battle cruisers. When his detected the USS Enterprise, L'Nar decided to ask Kirk's first officer Spock for assistance in his battle with the Klingon battlecruisers in exchange for the Kirk and his landing party. After Spock rescued his captain, L'Nar planned to hunt the Enterprise down after he wiped the Klingon fleet. However, the Section 31 agent onboard his ship, told him that the Enterprise belonged to them and warned him to choose his next move wisely. L'Nar then demanded the peaceful surrender of the Enterprise from commander Spock or he would destroy them. L'Nar was then contacted by the Section 31 agent aboard their ship and was told that their alliance was over. L'Nar then threatened to destroy both ships. However, L'Nar, his ship, and his others ships were then destroyed by a sleeper program installed with their weaponry that initiated self-destruct on all the Romulan ships. (TOS - The Khitomer Conflict comics: "Part 1", "Part 2", "Part 3", "Part 4")