Lambert

Lambert is a main character in The Witcher 3 who appears in 11 quests, including “Kaer Morhen” and “On Death's Bed”. Lambert plays Gwent with a Scoia'tael deck. Your first win against Lambert earns the card “Triss Merigold”. You can meet Lambert in Velen/Novigrad and Kaer Morhen as well as on Skellige.

From the journal

The youngest among the witchers of Kaer Morhen, and perhaps the last ever trained within its walls, by the start of our tale Lambert had proven his chops many times over, having hunted down many a mighty beast and traversed nearly all the Continent's realms several times over.

Yet he had also developed a reputation for arrogance and sardonic humor, and his gruff and at times excessively blunt manner could irritate even his fellow witchers of the School of the Wolf. Whatever his vices, it went without saying that Lambert would brave the fires of any hell for his companions.

If destiny truly chooses which boys become witchers, then in Lambert’s case it had made a twisted, cruel choice. After hearing his story, Geralt had to admit that Lambert had every reason to be unenthused about the lot fate had granted him.

Read on (6 paragraphs) – reveals how the story continues

A chance encounter of two witchers hunting the same ekimmara turned into a tale of old friendship, murder and vengeance. The moral of the story? Don't mess with Lambert.

Though Lambert made no secret of his hatred for Kaer Morhen, when the time came to stand in its defense, he did so without a second thought.

Sadly, during the battle Lambert found himself overwhelmed by enemy forces. Relief came too late and he was cut down by the Wild Hunt's warriors.

During this battle he came within a hair’s breadth of losing his life. Luckily, Geralt arrived in the nick of time and together they held back his attackers.

Depending on the outcome: … During this battle, he came within a hair’s breadth of losing his life. Luckily Keira arrived in the nick of time and together they held back his attackers.

It just might be that Lambert and Keira’s later (and somewhat unexpected) relationship came about as a result of that moment, when they fought for survival at each other’s side. It is also possible it was a simple matter of two attractive people taking a liking to each other. At any rate, only time could tell what would become of the couple.