Portrait artist Nelson Shanks died on August 28 at his home in Pennsylvania, the New York Times reports. The cause of death was prostate cancer.

Shanks was widely regarded for his commissioned portraits of political, social, and cultural leaders, notably Princess Diana, John Paul II, Ronald Reagan, Margaret Thatcher, and Luciano Pavarotti. He made headlines in 2015 for admitting that his 2001 portrait of president Bill Clinton—which was unveiled in 2006 and hung in the National Portrait Gallery for three years—holds a slick reference to the Monica Lewinsky scandal in the form of a shadow.

“The reality is [Clinton’s] probably the most famous liar of all time […] I could never get this Monica thing completely out of my mind and it is subtly incorporated in the painting,” he told the Philadelphia Inquirer.

Shanks was born in 1937 in Rochester, New York, but grew up in Wilmington, Delaware. He attended college at the University of Kansas, where he studied architecture before transferring to the nearby Kansas City Art Institute for painting. Shanks taught at the Memphis Art Institute, the School of the Art Institute of Chicago, the National Academy of Design, and the Art Students League.

Nelson Shanks’s official portrait of Bill Clinton contains a secret Monica Lewinksy reference. Courtesy of the artist.

He founded the Philadelphia art school Studio Incamminati with his wife Leona, who is also a painter, in 2002, where he continued to teach until the end of his life.

Shanks often created lasting friendships with the subjects of his portraits, especially Princess Diana. “Generally speaking, we make friends,” he noted in a 2013 interview. “And because I’m painting friends, their humanity is very much in the forefront…. They are part of the process, and they see what I’m doing the whole way. And I think they really, really gain from it.”