U.S. President Joe Biden held a private memorial service on Sunday to commemorate the 50th anniversary of the car crash that killed his first wife and their baby daughter.

President Biden and First Lady Jill Biden, alongside other members of the Biden family, attended mass at Saint Joseph on the Brandywine Roman Catholic Church in Wilmington, Delaware.

The gravesites of Biden’s first wife and infant daughter are located at Saint Joseph’s.

Mr. Biden was not in the car crash when a tractor-trailer hit his wife, 30-year-old Neilia, and their 13-month-old daughter Naomi, on December 18, 1972. Neilia had been out shopping to buy a Christmas tree. Beau and Hunter Biden, the couple’s two sons, were about to turn 4 and 3 at the time. The boys were in the car and seriously injured but both survived the crash.

Mr. Biden had just been elected to the Senate in November of that year.

At the time of the tragedy, Biden was 30 years old. He considered giving up his burgeoning political career, but after other senators advised him to stay in office, he remained a senator and began commuting from Washington to Delaware in order to be at home with his sons.

Neilia Biden graduated from Penn Hall in 1960 and later attended Syracuse University, where she studied law and was elected homecoming queen.

After the service on Sunday, the Bidens brought flowers to the gravesites of Neilia and Naomi.

President Biden married Jill Jacobs in 1977. Their daughter, Ashley, was born in 1981. Jill and Ashley joined Mr. Biden on Sunday, alongside Hunter and many of the president’s grandchildren, at the memorial service for Neilia and Naomi on Sunday.

Beau Biden, who died of brain cancer in 2015 at the age of 46, is also buried in the cemetery.