NEW YORK (Reuters) - Soon-to-be-jailed celebrity socialite Nicole Richie said she is pregnant by her boyfriend, singer Joel Madden of the rock band Good Charlotte.

"We are. I'm almost four months," said Richie, 25, in an interview with ABC's Diane Sawyer that will air on Thursday.

The waif-like daughter of singer Lionel Richie pleaded guilty on Friday to driving under the influence of drugs and was sentenced to four days in jail. She has been ordered to serve her time by Sept. 28 and put on three years probation.

"I have a responsibility and it's something that I did wrong, and if I could personally apologize to every single person that has lost a loved one from drunk driving I would," Richie said.

"Unfortunately I can't, but this is my way of paying my dues and taking responsibility and being an adult."

Richie rose to fame as hotel heiress Paris Hilton's co-star on the reality series "The Simple Life." Hilton spent three weeks behind bars in June for violating her probation in a drunken-driving case.

Richie was stopped in December when police said she was seen driving the wrong way on a Los Angeles freeway. Officers said she failed a field sobriety test and admitted she had smoked marijuana and taken prescription painkiller Vicodin.

Because of a 2003 DUI conviction, Richie had faced a mandatory sentence of up to a year in jail if found guilty in a trial but instead submitted her plea.