From the WTTW email we just received describing this evening's lead segment on Chicago Tonight:
Carol Marin sits down with a State Representative who will make a major personal announcement.
UPDATE (7:10 p.m.): State Rep. Deb Mell (D-Chicago) was the mystery guest. She appeared with her partner, Christin Parker, to announce their engagement and her intention to speak in support of gay marriage on the House floor tomorrow. She plans to ask her fellow lawmakers, "Please give us our rights." Added Parker, "We're not to be feared. There's nothing scary about allowing us to have the same rights as everyone else."
UPDATE (4/28): Capitol Fax has posted video of Mell's announcement on the House floor: