From A Wiki of Ice and Fire
|Title|| Steward of Highgarden|
Lord of Highgarden
Warden of the South
|Book(s)||A Game of Thrones|
When King Mern of the Reach died at the Field of Fire, Harlen Tyrell was but his steward. House Tyrell could claim descent from Garth Greenhand, but only through the female line. When Aegon I descended on Highgarden, Harlen Tyrell bent the knee and pledged fealty. For this, Aegon named him Lord of Highgarden and gave him dominion over the Reach.