Here's a nice timeline for people who are not totally aware of the reasons for the feud between these two icons.
Full article: http://www.ufc.com/news/ufc-145-timeline
10 June 2010: Rua suffers serious knee injury and rather than take interim bout, Evans decides to wait for his title shot. The fight is eventually set for March 2011
4 February 2011: News breaks that Evans is injured and will be unable to challenge the fully-healed ‘Shogun’ Rua for the UFC world light-heavyweight belt.
5 February 2011: Jones runs through fellow prospect and contender Ryan Bader with surprising ease and – with Evansʼs blessing – is offered the title fight vs Rua.
6 February 2011: Evans predicts Jones will “destroy” Rua in the first round of their light-heavyweight title fight.
10 February 2011: Asked repeatedly, Evans claims he will move division rather than face Jones should his ʻbrotherʼ win.
3 March 2011: During the broadcast of UFC Live: Sanchez vs. Kampmann, Jones said: “I respect (UFC President) Dana White a lot and, if that’s what he absolutely wanted (the Rashad fight) to happen, then I guess that’s what would have to happen.”
4 March 2011: Asked to respond on MMA Live, a visibly upset Evans said: “I am no punk. If Jon wins the (title) I got to sit down with the team and decide what to do.”
19 March 2011: Jones becomes the youngest UFC world champion in history, destroying Rua before going nose to nose with Evans in the Octagon.
19 March 2011: Speaking with MMA Fighting, Evans stuns the MMA world, announcing he has left Team Jackson. “I’m done with Jackson’s. And I know how to fight Jon. I trained with him for a long time.”
22 March 2011: Evans relocates his training camp to Imperial Athletics in Boca Raton, Florida forming the soon to be feared ʻBlackziliansʼ camp.
25 April 2011: It is announced that Jones has torn a ligament in his right hand, forcing him to withdraw from a proposed title defense against Evans.
April 27 2011: This time, Evans does not want to wait for the champion, and accepts a fight with replacement Phil Davis.
12 May 2011: Evans and Jones nearly come to blows at Surrender, a Las Vegas nightclub and they are separated byGeorges St-Pierre.
15 May 2011: Evans questions the legitimacy of Jones’ hand injury. “Jon doesn’t need surgery,” he said. “No doctor will operate on him. They say he doesn’t need it.”
13 July 2011: Another bitter pill for ʻSugaʼ as Davis pulls out of his fight with Evans with a knee injury.
6 August 2011: Eager to fight somebody – anybody – Evans eventually goes on to defeat Tito Ortiz inside two rounds,looking better than ever.
24 September 2011: Jones submits ‘Rampage’ in the fourth round of his first UFC world championship defense.
6 October 2011: Evans is forced to pull out of yet another date with Jones, due to a dislocated thumb injury picked up in his win over Ortiz.
10 December 2011: Jones caps off an incredible 2011 with a second successful title defense, this time against former champion Lyoto Machida.
28 January 2012: Evans easily defeats previously unbeaten Davis over five rounds in an eliminator bout to determine the next UFC title challenger.
30 January 2012: New emerges Evans picks up an injury – again – vs Davis and there is fear the already twice-postponed super-fight may
once again be off.
6 February 2012: Jon Jones vs Rashad Evans – perhaps the biggest 205lbs title fight since Liddell vs Ortiz II – is on. The fight is set for Atlanta in April.
16 February 2012: Cutting barbs are exchanged by the former friends at the official UFC 145 press conference in Atlanta. Jones accuses Evans of jealousy while ʻSugaʼ said ʻBonesʼ is ʻall fakeʼ.
18 February 2012: After months of saying he will not coach against his former star pupil, Greg Jackson confirms that he will corner Jones against Evans.
21 April 2012: Jon Jones and Rashad Evans will finally set to meet and settle their feud, once and for all, at UFC 145 in Atlanta, Georgia.