By Keith Idec

The WBO announced Thursday through its Twitter account that it has made Terence Crawford the mandatory challenger for WBO welterweight champion Jeff Horn.

The sanctioning organization also announced that representatives for Crawford and Horn must schedule their fight for within 90 days after Horn’s optional defense December 13 in Brisbane, Australia. Bob Arum’s Top Rank Inc. is Crawford’s promoter and Horn’s co-promoter, thus the deal should be relatively easy to complete.

The WBO’s announcement officially signaled Crawford’s move from 140 pounds to 147 and ended the undefeated Crawford’s reign as boxing’s undisputed super lightweight champion.

Before scheduling what will be an extremely difficult fight against Crawford, Australia’s Horn (17-0-1, 11 KOs) must first defeat England’s Gary Corcoran on December 13 at the Brisbane Convention Centre. Horn, 29, will make the first defense of the WBO title he won from Filipino superstar Manny Pacquiao (59-7-2, 38 KOs) on July 2 in Brisbane when he faces the 10th-ranked Corcoran (17-1, 7 KOs).

The 30-year-old Crawford (32-0, 23 KOs) is not expected to fight again until he challenges Horn for the WBO welterweight title.

The Omaha, Nebraska, native became boxing’s undisputed 140-pound champion in his last fight. By knocking out Namibia’s Julius Indongo (22-1, 11 KOs) in the third round August 19 in Lincoln, Nebraska, Crawford defended his WBC and WBO titles and won the IBF, IBO and WBA championships from Indongo.

That impressive victory made Crawford the first undisputed champion in any division since Jermain Taylor won the IBF, WBA, WBC and WBO middleweight titles from Bernard Hopkins in July 2005.

Now that Andre Ward has retired, Crawford is the No. 1-ranked fighter on most credible pound-for-pound lists.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.