Emotional detail spotted during Princess Ingrid Alexandra's appearance on historic day

Princess Ingrid Alexandra has paid a touching tribute to her grandmother Queen Sonja on the day her father King Haakon VIII officially took his oath to the Constitution before Parliament.

On Tuesday (1 September), the 22-year-old Norwegian royal made history in the wake of her grandfather King Harald V’s death on Friday (28 August), when she became crown princess and the first female heir to the throne in more than 600 years.

The last woman to rule Norway was Queen Margaret I, who sat on the throne between 1388 and 1412.

Now, Princess Ingrid takes on the important duty, while her father has become King Haakon VIII and her mother has become Queen Mette-Marit.

She broke tradition for a second time when she accompanied the new King to the official swearing-in ceremony in Oslo parliament, and signed the oath too, under Article 44, which outlines that any person of legal age who becomes first in line to the throne has to take a written oath before the Storting.

The Crown Princess wore a traditional mourning dress to the oath-taking ceremony (Lise Åserud/NTB/AFP via Getty Images)

And as we say, she also took the moment to sweetly pay homage to her grandmother Queen Sonja, 89, who was married to the late King Harald V for 57 years.

Wearing an elegant, floor-length black mourning dress for the historic day on Tuesday, Ingrid mirrored her grandmother’s look from more than two decades ago.

Queen Sonja wore a strikingly similar look when she attended the 1991 proclamation of King Harald V.

She also wore the same accessories - a black veil and headband, and the Grand Cross sash of the Order of St Olav.

Queen Sonja was there to see her son officially sign the oath to become King this week, as he declared in Norwegian: "I promise and swear to govern the Kingdom of Norway in accordance with its constitution and laws, so help me God the Almighty and the All-Knowing!"

The new ruler added: “The Queen and I confirm that we are available to carry out our duty for the country and the people."

King Harald was on the throne for 35 years and broke tradition when he chose to marry Sonja.

Traditionally, European heirs are expected to marry women from other royal or aristocratic families.

Ingrid's look almost directly mirrored that of her grandmother during King Harald's 1991 ceremony (INGE GJELLESVIK/Getty Images)

Sonja came from a middle-class Norwegian family and had no royal or noble title.

She included an emotional note on a ribbon she placed on her late husband’s coffin, which bore her personal monogram alongside a message in Norwegian that translates in English to ‘thank you for a good life.’

Norway’s royal palace confirmed over the weekend that King Harald’s funeral will take place on Wednesday, 9 September.

The country is in a state of mourning, and tens of thousands of Norwegians have expressed their grief over the weekend by laying flowers, writing cards and lighting candles in front of the royal palace in Oslo, where the coffin arrived late Friday from hospital.

Haakon said in his first speech as King that was broadcast live on public television: “I’m going to miss him. I’ll miss his laughter. His good-natured way of dealing with people and situations.

“That means, in the ultimate sense, being willing to risk everything, even one’s life, for Norway’s freedom and independence.”