Belgian's former king Albert II on Friday gave his blessing to his once-secret illegitimate daughter being welcomed into the royal family, saying he hoped for "better days" ahead.
The current King Philippe met his half-sister Delphine de Saxe-Cobourg for the first time last week, after a court ruled she was entitled to take her father's family name and the title princess.
Philippe and Delphine said in a joint statement that the meeting was "warm" and Delphine would build a relationship with them "in a family framework".
In a statement signed simply "Albert", the current monarch's father on Friday backed the move.
"I unreservedly endorse the communique that the King and Princess Delphine have published and I join in the spirit of this message," he said.
"My wife and I are very happy with what has been achieved on the King's initiative, the first steps towards better days for everyone and especially for Delphine."
It marks a dramatic conversion for Albert, 86, who spent decades denying his paternity until a court ordered a DNA test in 2019.
This confirmed he was indeed Delphine's biological father, which he had refused to admit since the revelation in 1999 of an old extra-marital affair.
But Albert, who ruled from 1993 to 2013, continued to show his daughter the cold shoulder and the rejection prompted Delphine to seek recognition through the courts.
A Belgian court ruled on October 1 that the 52-year-old artist had the right to call herself princess and use the royal family name.
Delphine was born in 1968 to a baroness, Sibylle de Selys Longchamps, and future king Albert early during an affair that lasted until 1984.
Albert had already married his future queen, Paola, and the illegitimate daughter was kept secret.