CHICAGO-Simon Property Group formally announced its "best and final offer" to takeover or help reorganize locally-based General Growth Properties Thursday. Simon released a letter sent that day to GGP officers with a promise of paying $6.5 billion, or about $20 per share for the company, slightly more than $4 per share higher than GGP stock closed at on Thursday at $15.80.

It was labeled a last offer because GGP is scheduled to appear this morning before US Bankruptcy Court Judge Allan Gropper, of the New York Southern District, to decide between Simon’s offer and a reorganization plan proposed by Toronto-based Brookfield Asset Management. General Growth has said repeatedly that it favors the Brookfield plan, but Simon has also increased its bid several times, starting from $9 per share in early February.

In the Thursday letter, David Simon, chairman and CEO, says his firm will completely back out of the bidding process if GGP decides today that it will still stay with the Brookfield plan. However, Simon said that it’s not likely shareholders will see $20 a share again, and that GGP officers should give his offer more thought, even if it means postponing today’s hearing for another week. The hearing has been set back a number of times already, in part for more time to consider Simon vs. Brookfield proposals .

Blackstone Real Estate Advisors has pledged to help fund Simon’s latest takeover proposal. However, as GGP has been leery to turn over its large mall portfolio to its main competitor, and there’s also anti-trust issues, Simon has said he could also match all of Brookfield’s reorganization promises, without the millions of dollars of warrant fees Brookfield will charge as part of the transaction. Simon said he is standing by to activate either plan as necessary to join with GGP. "Time is short," Simon said in the letter. "We urge you to seize the moment to achieve the best result for GGP and its stakeholders."