The royal couple and Queen Margrethe of Denmark will be among the guests at a number of events in Sweden to mark the king's 50th year on the throne.
Crown Prince Frederik is also godfather to Victoria and Daniel's son and youngest child, Prince Oscar.
It's not known which events specifically the Danish royals will attend, but on Thursday 14 September, there will be a performance at Drottningholm Palace Theatre, followed by a reception and a private dinner at the palace.
Friday will begin with a Te Deum at the Royal Chapel of Stockholm Palace, with the King later overseeing the Changing of the Guard. A banquet will then be held at the Rikssalen of Stockholm Palace in the evening.
Celebrations will conclude on Saturday 16 September with a carriage procession through Stockholm, followed by a concert at Norrbro.
A number of royals from other European households have also confirmed their attendance at King Carl's Jubilee celebrations.
Queen Margrethe's sister, Queen Anne-Marie of Greece, who is also a first cousin of the king, will be among the guests, as well as Norway's King Harald V, Queen Sonja, Crown Prince Haakon and Crown Princess Mette-Marit.
King Carl XVI Gustaf, 77, who ascended the throne on 15 September 1973, married wife Silvia in 1976.
King Carl and Queen Silvia have eight grandchildren – Victoria's children, Princess Estelle and Prince Oscar, Prince Carl's sons, Prince Alexander, Prince Gabriel and Prince Julian, and Princess Madeleine's kids, Princess Leonore, Prince Nicolas and Princess Adrienne.
As of November 2019, Prince Carl Philip and Princess Madeleine's children are no longer styled His/Her Royal Highness as part of a move by King Carl to strictly associate Swedish royalty to the office of the head of state.
The young royals are not expected to carry out public duties in future, and will be able to carve out their own careers.