[4] After five years of fighting at smaller Dutch events, Leroy Kaestner made his K-1 debut at the K-1 World MAX 2009 Europe Tournament in Utrecht, Netherlands on March 1, 2009, becoming the surprise winner of the competition, beating Marco Pique in the final by unanimous decision.
As a result of his victory Kaestner would qualify for the K-1 World MAX 2009 Final 16, losing by decision to eventual runner up Andy Souwer.
Kaestner's performance against Souwer would lead to him being invited to the K-1 World MAX 2009 Final 8 as a reservist, although he would lose his bout to local fighter Yasuhiro Kido.
Since that tournament Leroy has continued his progress claiming a notable win over K-1 MAX finalist Gago Drago at It's Showtime 2010 Amsterdam.
At the end of 2010, Kaestner won his second major title by defeating Cagri Ermis to win the W.F.C.A.