http://intouchweekly.hollywood.com/2008/02/the_secret_marykate_knew_about.php

Heath Ledger and Mary-Kate Olsen were more than just friends. “Mary-Kate was no stranger to his apartment,” an insider says. “They were dating.” While they weren’t serious, Heath liked MK’s sense of humor. “Heath was amused by this teeny little thing bursting with nervous energy and smoking like a chimney,” a pal says. But there was also a dark side to their chemistry. “To put it bluntly, both of them had a mutual interest in partying,” says the insider. “She could drink a lot for someone her size,” says a friend who partied with her at Hyde and Les Deux in LA. At the Sundance Film Festival in Utah in January, witnesses tell In Touch that Mary-Kate was chain-smoking, downed seven beers in two hours and fell down at a party hosted by 5WR and Butter. “She was so drunk,” an onlooker says. “She could barley stand up.”

For more on Mary-Kate’s involvement in Heath’s death, pick up In Touch.