They are pictured next to a poster of the 1942 classic film "Casablanca", Hugh's favorite movie, reported E!Online.
"Happy 90th to a man with a heart of gold. @hughhefner #casablancanight," Crystal wrote.
Hefner and his wife, his third, have been married since 2012. They wed at the Playboy Mansion.
Hugh has hosted a Casablanca-themed party at his famous home on his birthday in years past and continued the tradition
"Tonight for my Birthday, we will be watching my all time favorite movie 'Casablanca' with friends and family," he tweeted.