W.A.K.O. World Championships 1981 were the third world kickboxing championships hosted by W.A.K.O. and were organized by Italian Ennio Falsoni.
 It was the second time that W.A.K.O. had held a championships in Italy (the Europeans had been held there in 1979) and heralded the beginning of the organizations having its world championships every two years as opposed to once a year.
 The event was open to amateur men only from across the world, and featured two categories; Semi-Contact kickboxing and the newly introduced Musical Forms, and for the first time ever there was no Full-Contact kickboxing.
 By the end of the championships, West Germany were the top nation, with the USA in second and host nation Italy in third.
 The event was held in Milan, Italy in 1981.
Hereditary peers form part of the peerage in the United Kingdom.
 There are over eight hundred peers who hold titles that may be inherited.
 Formerly, most of them were entitled to sit in the House of Lords, but since the House of Lords Act 1999 was passed, only 92 are permitted to do so, unless they are also a life peer.
 Peers are called to the House of Lords with a writ of summons.
Valentijn Overeem (] ; born 17 August 1976) is a Dutch professional mixed martial artist and kickboxer currently signed with United Glory.
 A professional competitor since 1996, he has previously fought for the PRIDE Fighting Championships, RINGS, KSW, the World Fighting Alliance, K-1, M-1 Global, Its Showtime, World Victory Road, and Strikeforce.
 He is the older brother of fellow MMA fighter Alistair Overeem.
The World Association of Kickboxing Organizations (W.A.K.O or WAKO) is an international organization of kickboxing.
 The governing body of amateur kickboxing certified by WAKO is created to develop support and govern at an amateur level In addition to holding world championship events, WAKO sanctions the champions of kickboxing.
Eduard Mammadov (born January 2, 1978, in Baku) is an Azerbaijani kickboxer, nicknamed the "White Wolf".
 He is a current fourteen times World Association of Kickboxing Organizations World Heavyweight Low Kick Champion and the European World Kickboxing Heavyweight Champion.
Felipe Stievano Micheletti (born May 24, 1990) is a Brazilian professional kickboxer who fights in the heavyweight class.
 Before signing with the Kunlun in 2017, Micheletti has fought for the Superkombat World Grand Prix (WGP) kickboxing organizations.
The Montenegrin nobility (1852-1918) are notable people of the Principality of Montenegro and the Kingdom of Montenegro who hold titles such as "knez" (prince), "vojvoda" (duke), "veliki vojvoda" (grand duke), "serdar" (count), and "guvernadur" (governor).
 The titles are hereditary or for life.
 Focusing on the Montenegrin nobility of the late 19th century surrounding the then recent secularisation of the principality under Danilo II and his court, excluding the older traditional clan nobility.
Alistair Cees Overeem (] , ; born 17 May 1980) is a Dutch mixed martial artist and former kickboxer.
 He is a former Strikeforce Heavyweight Champion, DREAM Interim Heavyweight Champion, K-1 World Grand Prix Champion, and is one of only two fighters to hold world titles in both MMA and K-1 kickboxing at the same time.
Bridgett Riley (born May 13, 1973) is a female boxer and motion picture stuntwoman from Oakville, Missouri.
 While working as an airline attendant, she decided to learn martial arts.
 The interest in the sport came from her brother Patrick's strong interest in mixed martial arts.
 She trained with her brother and a number of other high-profile martial artists early in her career.
 Notably, she was trained by former three time world kickboxing champion, Jim Boucher (Belleville, IL).
 She was a member of a competition team with other competitors such as: Ronnie "Diamond" Deleon (World Kickboxing Champion), Patrick Riley (mixed martial arts champion), Donny Reinhardt (world champion), Russ Hogue (US Kickboxing Champion).
WAKO Pro World Grand Prix, was a kickboxing promotion featuring events held in between national teams since 2011 by the WAKO-Pro organization in association with national kickboxing organizations.

Question: What two kickboxing organizations did the brother of Valentin Overeem hold titles in at the same time?
Answer: MMA and K-1