[2][3] The design and colours of the Swedish flag are believed to have been inspired by the present coat of arms of Sweden of 1442, which is blue divided quarterly by a cross pattée of gold.

The Royal flag (Kungliga flaggan) is identical to the triple-tailed naval ensign, but has in its centre a white field with the greater or the lesser coat of arms surrounded by the Order of the Seraphim, which has the monarch as its grand master.

[8] According to early modern legend, the 12th-century King Eric IX saw a golden cross in the sky as he landed in Finland during the First Swedish Crusade in 1157.

According to this theory,[citation needed] the Swedish flag was created during the reign of King Charles VIII, who also introduced the coat of arms of Sweden in 1442.

The exact age of the Swedish flag is not known, but the oldest recorded pictures of a blue cloth with a yellow cross date from the early 16th century, during the reign of King Gustav I.

[citation needed] The first legal description of the flag was made in a royal warrant of 19 April 1562 as "yellow in a cross fashioned on blue".

Prior to this, a similar flag appeared in the coat of arms of King John III's duchy, which is today Southwest Finland.

[1] According to the same royal warrant, merchant ships were only allowed to fly square-cut city flags in their respective provincial colours.

In a government instruction of ship building of 1730, this civil ensign should have the same proportions and colors as the state flag, with the notable difference of being square-cut.

This flag was identical to the former triple-tailed military ensign of Sweden, with a white saltire on red to be included in the canton.

Following the adoption of a separate Norwegian flag, a royal regulation of 17 July 1821, stipulated that ships of both kingdoms use the common square-cut civil ensign (with the saltire included) in "distant waters" (i.e. beyond Cape Finisterre).

A royal resolution of 20 June 1844, introduced new flags and heraldry to denote the equal status of the two kingdoms within the union.

The warrant also stipulated that the merchant fleet use their respective countries' square-cut civil ensigns, including the new union mark.

In Sweden, however, the new union mark in particular became quite unpopular and was contemptuously nicknamed the Sillsallaten (Swedish) or Sildesalaten (Norwegian) after a colorful dish of pickled herring, decorated with red beets and apples in a radial pattern.

The military ensign was also to be used by civil government ships and buildings, such as the Customs, Harbor pilots and the Royal Mail.

During the 1890s, two consecutive sessions of the Norwegian parliament voted to abolish the mark, but the decision was overruled by royal veto.

On naval ships the flag of the king is raised together with a split pennant with the greater national coat of arms.

Likewise the flag of the heir apparent is raised together with a split pennant with the lesser national coat of arms on naval ships.

The government therefore ordered the speaker of the Riksdag, Ingemund Bengtsson, to serve as regent ad interim for two days.

There is also an unofficial version of the pennant which resembles the national flag, with a yellow cross on a blue field, which is advised not to be used.