Danish Queen Margrethe II Celebrates Her 78th Birthday at the Palace on April 16, 2018 in Copenhagen, Denmark.

The late Prince Henrik, pictured in 2017, was married to Queen Margrethe II of Denmark for over 50 years, until his death on 13 February 2018.

Queen Margrethe II of Denmark all smiles, marked her 78th birthday in Copenhagen on Monday. She has been on the throne since January 1972

Crown Prince Frederik was not seen on the palace balcony on Monday-April 16, 2018, but his wife and their four children were at his mother's side on her birthday from left to right: Princess Isabella, Princess Josephine, Crown Princess Mary of Denmark, Prince Vincent and Prince Christian.

Crown Princess Mary, wearing a red dress, stood proudly behind her children, (left to right) Princess Isabella, twins Princess Josephine and Prince Vincent, and Prince Christian

Queen Margrethe II of Denmark beamed and waved to the crowds from the balcony of the palace, as she marked her 78th birthday in Copenhagen

Queen Margrethe II of Denmark wore a vibrant blue blouse beneath a pin-striped belted jacket and matched her earrings to her blue top

Queen Margrethe II was seen smiling at her seven-year-old grandson, Prince Vincent (front-left) on the palace balcony alongside with her other grandchildren Princess Isabella (back left), Prince Felix and Princess Athena (R)

(L-R) Denmark's Princess Josephine, Princess Isabella, Prince Christian, Prince Vincent, Crown Princess Mary, Queen Margrethe II, Princess Marie, Prince Nikolai, Princess Athena, and Prince Henrik pose on the balcony of Amalienborg palace during the Danish Queen's 78th Birthday celebrations on April 16, 2018, in Copenhagen, Denmark.

Denmark's Queen Margrethe, who turned 78 on Monday, seen center, was joined on the balcony by (from left) Princess Josephine, Princess Isabella, Crown Princess Mary, Prince Vincent, Prince Christian, Princess Marie, Prince Joachim (just seen), Princess Athena, Prince Felix, Prince Nikolai, and Prince Henrik

Princess Josephine of Denmark, wearing a tweed coat dress and with a smart navy blue band in her hair on the balcony of Amalienborg Palace to marked her grandmother Queen Margrethe II 78th birthday in Copenhagen

Crown Princess Mary looked glamorous in a red dress, surrounded by her children from left to right: Princess Isabella, the twins Princess Josephine and Prince Vincent, and Prince Christian

(L-R) Playful Princess Josephine cheekily covered her eyes as her brothers and sister waved from the balcony, Princess Isabella, Crown Princess Mary, Prince Christian and Prince Vincent of Denmark

Princess Josephine of Denmark, wearing a tweed coat dress and with a smart navy blue band in her hair, did eventually offer a wave - albeit with a very solemn expression on her face

Dapper Princes Josephine's twin brother Prince Vincent (below left) delivered an angelic performance for the cameras, while his mother Crown Princess Mary (center left) and grandmother Queen Margrethe II were snapped smiling proudly at him and his older brother

Well-wishers gathered at the palace in Copenhagen waved Danish flags as they cheered for their Queen Margrethe II on her 78th birthday

(L-R) Princess Josephine is seen with her older sister, Princess Isabella on the balcony of Amalienborg Palace in Copenhagen.

The seven-year-old Princess Josephine appeared to stifle a yawn at one point as the royal family posed for photographs on the balcony of the palace in Copenhagen

(L-R) Princess Josephine's antics were eventually spotted by her laughing older sister, Princess Isabella, who quickly urged her younger sibling to uncover her eyes, while the twin brother Prince Vincent delivered an angelic performance for the cameras

Prince Christian appeared to gently remove something from his little brother Prince Vincent's face behind them is their mother Crown Princess Mary of Denmark

Denmark's Prince Christian lent his younger brother Prince Vincent a helping hand at one point after he apparently caught something in his eye

The Queen's younger son Prince Joachim (far right), was joined on the balcony by his wife Princess Marie (far left), their children Princess Athena (second from left, in front), and Prince Henrik (third from left, in front), and Joachim's children from his first marriage; 18-year-old Prince Nikolai (third from left, behind), and 15-year-old Prince Felix (second from right)

Crown Princess Mary of Denmark together with her children from left-right Princess Josephine, Princess Isabella, Prince Christian and Prince Vincent appears at the balcony of the Royal residence, Amalienborg Palace, on the occasion of her 78th birthday of Queen Margrethe of Denmark on April 16, 2018, in Copenhagen, Denmark.

Crown Princess Mary of Denmark, Prince Christian of Denmark, Princess Isabella of Denmark, Prince Vincent of Denmark and Princess Josephine of Denmark pose on the balcony of Amalienborg palace during Queen Margrethe of Denmark's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

(R-L) Queen Margrethe of Denmark, Crown Princess Mary of Denmark, Prince Christian, Princess Isabella,  Princess Josephine and Prince Vincent pose on the balcony of Amalienborg palace during the Danish Queen's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

(R-L) Crown Princess Mary of Denmark with her children Prince Christian of Denmark, Princess Isabella of Denmark, Prince Vincent of Denmark and Princess Josephine of Denmark pose on the balcony of Amalienborg palace during Queen Margrethe of Denmark's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

(R-L) Crown Princess Mary of Denmark with her children Prince Christian of Denmark, Princess Isabella of Denmark, Prince Vincent of Denmark and Princess Josephine of Denmark pose on the balcony of Amalienborg palace during Queen Margrethe of Denmark's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

Crown Princess Mary of Denmark with her sons Prince Christian of Denmark, Princess and Prince Vincent of Denmark at the balcony of Amalienborg Palace in Copenhagen, Denmark

(R-L) Denmark's Queen Margrethe, Crown Princess Mary, Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine at the balcony of Amalienborg Palace in Copenhagen, Denmark. The Queen of Denmark celebrates her 78th birthday at the Palace.

Queen Margrethe of Denmark with grandchildren from left-right Prince Vincent, Princess Isabella, Prince Felix, Prince Christian and Princess Athena at the balcony of Amalienborg Palace in Copenhagen, Denmark. The Queen of Denmark celebrates her 78th birthday at the Palace.

(R-L) Crown Princess Mary of Denmark with her children Prince Christian of Denmark, Princess Isabella of Denmark, Prince Vincent of Denmark and Princess Josephine of Denmark pose on the balcony of Amalienborg palace during Queen Margrethe of Denmark's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

(R-L) Denmark's Prince Christian, Princess Isabella, Princess Josephine and Prince Vincent at the balcony of Amalienborg Palace in Copenhagen, Denmark.

(R-L) Denmark's Queen Margrethe, Crown Princess Mary, Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine at the balcony of Amalienborg Palace in Copenhagen, Denmark. The Queen of Denmark celebrates her 78th birthday at the Palace.

(L-R) Denmark's Princess Josephine, Princess Isabella, Prince Vincent, Prince Christian, Crown Princess Mary, Queen Margrethe II, Princess Marie, Prince Nikolai, Princess Athena and Prince Henrik at the balcony of Amalienborg Palace, to mark The Queen of Denmark 78th birthday in Copenhagen.

Queen Margrethe of Denmark marks her 78th birthday surrounded by her family from right to left Princess Marie, Crown Princess Mary, Prince Christian and Prince Vincent at the balcony of Amalienborg Palace in Copenhagen, Denmark.

Crown Princess Mary of Denmark with children Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine pose on the balcony of Amalienborg palace during Queen Margrethe of Denmark's 78th Birthday celebrations on April 16, 2018, in Copenhagen, Denmark.

Crown Princess Mary of Denmark with children Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine pose on the balcony of Amalienborg palace during Queen Margrethe of Denmark's 78th Birthday celebrations on April 16, 2018, in Copenhagen, Denmark.

Crown Princess Mary of Denmark with children Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine pose on the balcony of Amalienborg palace during Queen Margrethe of Denmark's 78th Birthday celebrations on April 16, 2018, in Copenhagen, Denmark.

(R-L) Denmark's Queen Margrethe, Crown Princess Mary, Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine at the balcony of Amalienborg Palace in Copenhagen, Denmark. The Queen of Denmark celebrates her 78th birthday at the Palace.

(R-L) Queen Margrethe of Denmark, Crown Princess Mary of Denmark, Prince Christian of Denmark and Prince Vincent of Denmark pose on the balcony of Amalienborg Palace during the Danish Queen's 78th Birthday celebrations on April 16, 2018, in Copenhagen, Denmark.

(R-L) Denmark's Queen Margrethe, Crown Princess Mary, Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine pose on the balcony of Amalienborg palace during the Danish Queen's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

(R-L) Denmark's Queen Margrethe, Crown Princess Mary, Prince Christian, Princess Isabella, Prince Vincent and Princess Josephine pose on the balcony of Amalienborg palace during the Danish Queen's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

Denmark's Crown Princess Mary looked glamorous in a red dress, surrounded by her children Prince Christian and Prince Vincent (front) pose on the balcony of Amalienborg palace during the Danish Queen's 78th Birthday celebrations 2018 in Copenhagen, Denmark.

Queen Margrethe II of Denmark wore a vibrant blue blouse beneath a pin-striped belted jacket, and matched her earrings to her blue top, as she marked her 78th birthday without her spouse of 50 years, beaming and waving from the balcony of Amalienborg Palace surrounded by loved ones.

Queen Margrethe of Denmark at the balcony of Amalienborg palace on April 16, 2018, in Copenhagen, Denmark. The Queen of Denmark celebrates her 78th birthday at the Palace.